Document:

<PAGE>   1
                                                                     EXHIBIT 4.6

                               FIRST AMENDMENT TO
                            NATCO PROFIT SHARING AND
                                  SAVINGS PLAN

     WHEREAS, National Tank Company (the "Company") has heretofore adopted and
maintains the NATCO Profit Sharing and Savings Plan (the "Plan"); and

     WHEREAS, the Plan was amended and restated, effective January 1, 1999; and

     WHEREAS, the Company desires to amend the Plan on behalf of itself and each
other employer designated as a participating employer under the Plan;

     NOW, THEREFORE, the Plan is hereby amended as follows, effective January 1,
2000:

     1. The name of the Plan shall be changed to "NATCO Group Profit Sharing and
Savings Plan."

     2. Section 3.2(b) of the Plan shall be deleted.

     3. The following new Section 3.8 shall be added to the Plan:

          3.8 FORM OF EMPLOYER CONTRIBUTION. Employer Contributions to the Plan
     may be made in the form of cash or shares of Company Stock or a combination
     thereof.

     4. The following new Paragraph (d) shall be added to Section 5.1 of the
Plan:

               (d) Notwithstanding the preceding paragraphs of this Section, to
     the extent Employer Contributions are made in the form of Company Stock,
     the Committee may require that such contributions remain invested in
     Company Stock for such period of time as it may determine in its sole
     discretion.

     EXECUTED this ____ day of _______________, 2000.

                                             NATIONAL TANK COMPANY

                                             By:
                                                --------------------------------<PAGE>   1
                                                                     EXHIBIT 4.7

                                      STOCK

                                 TRUST AGREEMENT

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                               TABLE
<TABLE>
<CAPTION>
ARTICLE
-------
<S>             <C>                                                <C>
FIRST:          Acceptance of Property..............................2

SECOND:         Investment Powers.  ................................2

THIRD:          Payments.  .........................................5

FOURTH:         Administrative Powers.  ............................6

FIFTH:          Insurance Company Contracts........................10

SIXTH:          Fiduciary Standards................................11

SEVENTH:        Prohibition of Diversion...........................12

EIGHTH:         Hold Harmless......................................13

NINTH:          Accounts...........................................14

TENTH:          Committee..........................................15

ELEVENTH:       Compensation and Expenses..........................15

TWELFTH:        Resignation of Trustee.............................16

THIRTEENTH:     Amendment..........................................16

FOURTEENTH:     Termination........................................17

FIFTEENTH:      Plan-to-Plan Transfers; Rollovers..................18

SIXTEENTH:      Adopting Employers.................................18

SEVENTEENTH:    Alienation.........................................19

EIGHTEENTH:     Bond...............................................20

NINETEENTH:     Successors.  ......................................20

TWENTIETH:      Severability.......................................20

TWENTY-FIRST:   Communications.....................................20

TWENTY-SECOND:  Governing Law......................................21
</TABLE>

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                              STOCK TRUST AGREEMENT

     WHEREAS, the NATCO Profit Sharing and Savings Plan, hereinafter referred to
as the "Plan," was initially established with an effective date of September 1,
1989, by National Tank Company, hereinafter referred to as the "Company," for
the purpose of providing retirement and related benefits to eligible employees
of the Company and their beneficiaries, hereinafter referred to as
"Participants"; and

     WHEREAS, the Plan Committee, the members of which are "named fiduciaries"
as defined in the Employee Retirement Income Security Act of 1974, as amended
("ERISA"), (which named fiduciaries are hereinafter referred to as the
"Committee") has general responsibility for administration of the Plan; and

     WHEREAS, the Plan calls for the establishment of a trust to which
contributions are to be made by the Company to be held by the Trustee and to be
managed, invested and reinvested for the exclusive benefit of Participants of
the Plan and their beneficiaries; and

     WHEREAS, the Plan and trust are intended to qualify as a plan and trust
that meet the applicable requirements of Sections 401(a) and 501(a) of the
Internal Revenue Code of 1986, as amended, hereinafter referred to as the
"Code"; and

     WHEREAS, the current trustee of the Trust has resigned as trustee effective
March 1, 1999; and

     WHEREAS, effective March 1, 1999, the Company wishes to restate the
agreement of trust, hereinafter referred to as the "Trust," in its entirety and
appoint UMB Bank, N.A., a national banking association, having its principal
place of business at Kansas City, Missouri, hereinafter referred to as the
"Trustee"; and

     NOW, THEREFORE, in consideration of the premises and of the mutual
covenants herein contained, the Company and the Trustee do hereby covenant and
agree as follows:

<PAGE>   4

     FIRST: Acceptance of Property. The Trustee shall accept such cash and other
property as is tendered to it as contributions hereunder, and as is acceptable
to it, hereinafter referred to as the "Trust Fund," but shall not be under any
duty to require the Company or any other adopting employer to contribute to the
Trust Fund or to determine whether the amount of any contribution has been
correctly computed under the terms of the Plan. In no event shall the Trustee be
considered a party to the Plan. The Trustee shall have only such duties with
respect to the Plan as are set forth in this Agreement.

     SECOND: Investment Powers. The Trustee shall invest the assets of the Trust
Fund as directed by the Plan Administrator, Company, Committee, or Participants
in accordance with the provisions of the Plan. In doing so, the Trustee will be
a directed trustee. Trust investments may include, without limitation, employer
securities, as that term is defined in section 407(d) of ERISA, without regard
to limitations imposed by Section 407(a) of ERISA, and any fund created for the
collective investment of the assets of employee benefit trusts, as long as such
collective investment fund is a qualified trust under the applicable provisions
of the Code (and while any portion of the trust fund is so invested, such
collective investment fund shall constitute a part of the Plan, and the
instruments creating such fund shall constitute a part of this agreement). The
Trustee shall have no independent investment duties or responsibilities. The
Trustee assumes no financial responsibility with respect to the investment of
the assets of the Trust Fund. If the Trustee properly carries out such
investment directions, the Trustee will have no liability for any loss or
diminution in value occasioned thereby.

     To the maximum extent permitted by law, the Trustee shall not be liable for
the acquisition, retention or disposition of any assets of the Trust Fund or for
any loss to or diminution of such assets

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unless due to the Trustee's own negligence or willful misconduct.

     The Committee may appoint an "investment manager," as defined in Section
3(38) of ERISA. Any investment manager so appointed shall be (i) an investment
adviser registered as such under the Investment Advisers Act of 1940, (ii) not
registered as an investment adviser under such act by reason of paragraph (1) of
section 203A(a) of such act, is registered as an investment adviser under the
laws of the state (referred to in such paragraph (1)) in which it maintains its
principal office and place of business, and, at the time it last filed the
registration form most recently filed by it with such state in order to maintain
its registration under the laws of such state, also filed a copy of such form
with the Secretary of Labor, (iii) a bank, or (iv) an insurance company
qualified to perform investment management services under the laws of more than
one state of the United States. The Committee shall notify the Trustee of any
such appointment by delivering to the Trustee an executed copy of the instrument
under which the investment manager is appointed and evidencing the investment
manager's acceptance of such appointment, an acknowledgment by the investment
manager that it is a fiduciary of the Plan, and a certificate evidencing the
investment manager's current registration under the Investment Advisers Act of
1940 or other appropriate qualification. The Committee shall specify to the
Trustee the portion of the Trust Fund that shall be subject to such investment
management. The Trustee shall invest and reinvest the portion of the Trust Fund
subject to such investment management only to the extent and in the manner
directed by the investment manager in writing. During the term of such
appointment, the Trustee shall have no liability for the acts or omissions of
such investment manager, and except as provided in the preceding sentence, shall
be under no obligation to invest or otherwise manage the portion of the Trust
Fund subject to such investment management. The Trustee may maintain separate
accounts within the Trust Fund

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for the assets of the Trust Fund subject to such investment management. The
Committee may terminate its appointment of an investment manager at any time and
shall notify the Trustee in writing of such termination. To the maximum extent
permitted by ERISA, the Trustee shall be protected in assuming that the
appointment of an investment manager remains in effect until it is otherwise
notified in writing by the Committee.

     In the event that the investment manager appointed hereunder is a bank or a
trust company, or an affiliate of a bank or a trust company, the Trustee shall,
upon the direction of the Committee, transfer funds to such bank, trust company,
or affiliate for investment through the medium of any fund created and
administered by such bank, trust company, or affiliate, acting as trustee
therefore, for the collective investment of the assets of employee benefit
trusts, provided that such fund is qualified under the applicable provisions of
the Code and while any portion of the assets are so invested, such fund shall
constitute part of the applicable plan or plans, and the instrument creating
such fund shall constitute part of this Trust. In order to implement the
provisions of this paragraph, the Trustee is authorized to enter into any
required ancillary trust, agency or other type of agreement with an investment
manager, or its affiliate, as described in the preceding sentence.

     Except in the event of a tender or exchange offer as hereinafter provided,
or in the case of fractional shares received in any stock dividend, stock split
or other recapitalization or as necessary to make any distribution or payment
from the Trust Fund, or unless expressly prohibited by ERISA, the Trustee shall
have no power or duty to sell, tender, exchange or otherwise dispose of any of
the Company's common stock held in the Fund, hereinafter referred to as the
"Company Stock Fund." In the event that a tender or exchange offer is made for
all or any portion of the stock held in the Company Stock Fund, the Company
shall take such action as is practicable to provide each

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Participant in the Plan having an interest in such Fund with the same
information that is distributed by the Company to the stockholders of the
Company owning the same class of common stock for which such offer is made.
Notwithstanding any other provision of the Plan or this Trust Agreement, in the
event such an offer is made, each such Participant shall have the right to
direct the Trustee, by timely notice, to tender or exchange all or any portion
of the full shares of such common stock credited to this account, and the
Trustee shall so tender or exchange only upon receipt of such direction. If the
Trustee has not received timely directions from a Participant with respect to
whether or not to tender or exchange the shares of Company stock allocated to
such Participant's account, the Committee shall direct the Trustee whether or
not to tender or exchange such shares and the Trustee shall act in accordance
with such direction. In so acting, the Trustee shall be a directed trustee
without independent discretionary authority to tender or exchange stock held in
the Company Stock Fund. All property received in exchange for such common stock
so tendered shall upon receipt be held by the Trustee in the Fund within the
accounts of those Participants who so tendered, the provisions of the Plan and
this Trust Agreement shall hereby be deemed amended to permit the holding of
such property within said Fund and thereafter administered, invested, reinvested
and distributed in accordance with the applicable terms of the Plan and Trust.

     THIRD: Payments. Subject to the provisions of Article FOURTEENTH hereof,
the Trustee shall from time to time transfer cash or other property from the
Trust Fund to such persons, including an insurance company or companies or a
paying agent designated by the Committee, at such addresses, in such amounts,
for such purposes and in such manner as the Committee may direct, provided that
such transfer is administratively feasible, and the Trustee shall incur no
liability for any such payment made at the direction of the Committee. The
Committee shall be solely responsible

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to insure that any payment made at its direction conforms with the provisions of
the Plan, the provisions of this Agreement, and ERISA, and the Trustee shall
have no duty to determine the rights or benefits of any person in the Trust Fund
or under the Plan or to inquire into the right or power of the Committee to
direct any such payment.

     FOURTH: Administrative Powers. The Trustee is authorized to exercise from
time to time the following powers in respect of any property, real or personal,
of the Trust Fund, it being intended that these powers be construed in the
broadest possible manner:

     (1)  power to sell at public or private sale for cash or upon credit or
          partly for cash and partly upon credit and upon such terms and
          conditions as it shall deem proper. No purchaser shall be bound to see
          to or be liable for the application of the proceeds of any such sale;

     (2)  power to exchange securities or property held by it for other
          securities or property, or partly for such securities or property and
          partly for cash, and to exercise conversion, subscription, option and
          similar rights with respect to securities held by it, and to make
          payments in connection therewith;

     (3)  power to vote in person or by proxy at corporate or other meetings and
          to participate in or consent to any voting trust, reorganization,
          dissolution, merger or other action affecting securities in its
          possession or the issuers thereof; provided, however, to the extent
          required by Section 409(e) of the Code or Plan provisions, each
          Participant in the Plan who has an interest in the Company Stock Fund
          shall be entitled to direct the Trustee as to the manner in which the
          Company's stock having voting rights that is allocated

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          to such Participant's account is to be voted. The Trustee, itself or
          by its nominee, shall be entitled to vote and shall vote said stock
          with voting rights allocated to the accounts of said Participants as
          follows: (i) The Company shall adopt reasonable measures to notify
          said Participants of the date and purposes of each meeting of
          stockholders of the Company at which holders of shares of stock shall
          be entitled to vote, and to request instructions from such
          Participants to the Company, its agent or the Trustee as to the voting
          at such meeting of the number of shares of common stock (including
          fractional shares) in the account of each such Participant whether or
          not vested. (ii) In each case, the Trustee, itself or by proxy, shall
          vote the shares of said stock (including fractional shares) in the
          account of each such Participant in accordance with the directions of
          the Participant as communicated directly to the Trustee or to the
          Trustee by the Company or its agent. (iii) If prior to the time of
          such meeting of stockholders (or a date prior thereto specified by the
          Trustee), the Trustee shall not have received timely directions from a
          Participant as to the manner of voting any shares of allocated stock
          in the account of such Participant, the Trustee shall vote such shares
          as directed by the Committee. In so acting, the Trustee shall be a
          directed trustee without independent discretionary authority to vote
          shares of the Company's stock;

     (4)  power to acquire, hold or dispose of property in unregistered form, or
          in its name without designation of fiduciary capacity, or in the name
          of its nominee or any custodian, and to the extent permitted by ERISA,
          to combine

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          certificates representing investments with investments of the same
          issue held by the Trustee in other fiduciary capacities, and to
          deposit property in a depository or clearing corporation or with the
          federal reserve bank in its district;

     (5)  power to compromise and adjust all debts or claims due to or made
          against it, to participate in any plan of reorganization,
          consolidation, merger, combination, liquidation or other similar plan
          or any action thereunder, or any contract, lease, mortgage, purchase,
          sale or other action by any corporation or other entity;

     (6)  power to deposit any such property with any protective, reorganization
          or similar committee; to delegate discretionary power to any such
          committee; and to pay part of the expenses and compensation of any
          such committee; and any assessments levied with respect to any
          property so deposited;

     (7)  power to exercise any conversion privilege or subscription right
          available in connection with any such property; to oppose or to
          consent to the reorganization, consolidation, merger or readjustment
          of the finances of any corporation, company or association, or to the
          sale, mortgage, pledge or lease of the property of any corporation,
          company or association any of the securities of which may at any time
          be held in the Trust Fund and to do any act with reference thereto,
          including the exercise of options, the making of agreements or
          subscriptions and the payments of expenses, assessments or
          subscriptions, which may be deemed necessary or advisable in
          connection

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          therewith and to hold and retain any securities or other property
          which it may so acquire;

     (8)  power to make distributions in cash or in specific property, real or
          personal, or an undivided interest therein, or partly in cash and
          partly in such property;

     (9)  power to engage legal counsel, including counsel to the Company or the
          Trustee in its individual capacity, and any other suitable agents, and
          to consult with such counsel or agents with respect to the
          construction of this Agreement, the administration of the Trust Fund,
          and the duties of the Trustee hereunder;

     (10) power to commence or defend suits or legal proceedings and to
          represent the Trust Fund in all suits or legal proceedings; to settle,
          compromise or submit to arbitration any claims, debts or damages due
          or owing to or from the Trust Fund, provided that the Trustee shall
          notify the Committee of all such suits, legal proceedings and claims
          and, except in the case of a suit, legal proceeding or claim involving
          solely the Trustee's action or omissions to act, shall obtain the
          written consent of the Company before settling, compromising or
          submitting to binding arbitration any claim, suit or legal proceeding
          of any nature whatsoever;

     (11) power, upon the written direction of the Committee, to enter into any
          contract or policy with an insurance company or companies, for the
          purpose of insurance coverage or otherwise, provided that, except as
          provided in Article FIFTH, the Trustee shall be the sole owner of all
          such contracts or policies

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          and all such contracts or policies shall be held as assets of the
          Trust Fund;

     (12) power to make, execute and deliver, as Trustee, any and all deeds,
          leases, notes, bonds, guarantees, mortgages, conveyances, contracts,
          waivers, releases or other instruments in writing necessary or proper
          for the accomplishment of any of the foregoing powers;

     (13) power to transfer assets of the Trust Fund to a successor trustee as
          provided in Article TWELFTH; and

     (14) power to appoint custodians or subcustodians to hold any or all of the
          Trust Fund;

     (15) power to appoint ministerial agents to perform various functions of
          the Trustee; and

     (16) power to exercise, generally, any of the powers that an individual
          owner might exercise in connection with property either real, personal
          or mixed held by the Trust Fund, and to do all other acts that the
          Trustee may deem necessary or proper to carry out any of the powers
          set forth in this Article FOURTH or otherwise in the best interests of
          the Trust Fund.

Notwithstanding the foregoing, in the event that an investment manager is
appointed pursuant to Article SECOND hereof, such investment manager shall
exercise such of the powers enumerated in this Article FOURTH and otherwise
contained in this Agreement with respect to the portion of the Trust Fund
subject to its control as may be specified in the instrument under which the
investment manager was appointed.

     FIFTH: Insurance Company Contracts. The Trustee may, at the direction of
the Committee,

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(i) enter into one or more contracts with legal reserve life insurance
companies, the rate of return from which is fixed by the terms of such
contracts, (ii) transfer to any such insurance companies a portion of the Trust
Fund in accordance with any such contracts, and (iii) hold any such contracts as
a part of the Trust Fund until directed otherwise by the Committee. The
Committee shall give such direction to the Trustee by delivering to the Trustee
a copy of the action of the Committee signed by at least two members thereof,
which shall specifically refer to this Article FIFTH and direct the Trustee to
so act. The Committee may direct the Trustee to (i) request any information from
any such insurance companies necessary or appropriate to make an investment
decision, (ii) demand or accept withdrawals or other distributions under any
such contracts, (iii) exercise or not to exercise any rights, powers, privileges
and options under any such contracts and (iv) assign, amend, modify or terminate
any such contracts. The Trustee shall take no action with respect to any such
contracts except at the direction of the Committee. The Trustee shall incur no
liability for complying with or failing to comply with any direction of the
Committee. Any insurance companies issuing any contracts as hereinabove
described may deal with the Trustee as the absolute owner of any such contracts
and need not inquire as to the authority of the Trustee to act with regard to
such contracts. Any such insurance company may accept and rely upon any
communication from the Trustee that is signed by an officer of the Trustee. For
purposes of this Agreement, any such insurance company shall be considered to be
an investment manager with regard to the assets of the Plan subject to its
control. In no event shall the underlying assets of such insurance company in
which such contracts are invested be considered assets of the Plan or part of
the Trust Fund.

     SIXTH: Fiduciary Standards. The Trustee (or any investment manager
appointed pursuant to Article SECOND hereof) shall (i) discharge its duties
hereunder with the care, skill, prudence and

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diligence under the circumstances then prevailing that a prudent man acting in a
like capacity and familiar with such matters would use in the conduct of an
enterprise of a like character and with like aims; (ii) subject to the
investment funds specified in the Plan, if any, and to the extent required by
ERISA, diversify the investments of the Trust Fund so as to minimize the risk of
large losses unless under the circumstances it is clearly prudent not to do so;
and (iii) discharge its duties in accordance with the provisions of the Plan and
this Agreement insofar as such provisions are consistent with ERISA.

     The Trustee (or any investment manager appointed pursuant to Article SECOND
hereof) shall not engage in any transaction that it knows or should know
violates Section 406 of ERISA. Notwithstanding the foregoing, the Trustee (or
any investment manager appointed pursuant to Article SECOND hereof) may, in
accordance with any appropriate exemption provided under ERISA or upon the
approval of the Secretary of the Department of Labor, enter into any transaction
otherwise prohibited under Section 406 of ERISA.

     The Trustee shall not be responsible for the administration of the Plan,
for determining the funding policy of the Plan, or the adequacy of the Trust
Fund to meet and discharge liabilities under the Plan.

     The Trustee shall not be responsible for any failure of the Committee or
the Company to discharge any of their respective responsibilities with respect
to the Plan nor be required to enforce payment of any contributions to the Trust
Fund.

     SEVENTH: Prohibition of Diversion.

     (a)  At no time prior to the satisfaction of all liabilities with respect
          to Participants in the Plan and their beneficiaries shall any part of
          the corpus or

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          income of the Trust Fund be used for, or diverted to, purposes other
          than for the exclusive benefit of such Participants and their
          beneficiaries. Except as provided in paragraphs (b), (c) and (d)
          below, and Article THIRTEENTH, the assets of the Trust Fund shall
          never inure to the benefit of the Company and shall be held for the
          exclusive purpose of providing benefits to Participants in the Plan
          and their beneficiaries and defraying the reasonable expenses of
          administering the Plan.

     (b)  In the case of a contribution that is made by the Company by a mistake
          of fact, paragraph (a) above shall not prohibit the return to the
          Company of such contribution at the direction of the Committee within
          one year after the payment of the contribution.

     (c)  If a contribution by the Company is expressly conditioned upon the
          deductibility of the contribution under Section 404 of the Code, then
          to the extent such deduction is disallowed, paragraph (a) above shall
          not prohibit the return to the Company of such contribution at the
          direction of the Committee, to the extent disallowed, within one year
          after the date of such disallowance.

     EIGHTH: Hold Harmless. To the maximum extent permitted by ERISA and other
applicable law, the Trustee shall not be liable for and the Company shall
indemnify the Trustee against, and agrees to hold the Trustee harmless from, all
liabilities and claims (including attorney's fees and expenses in defending
against such liabilities and claims) against the Trustee, arising from the
Trustee's performance of its duties in conformance with the terms of the Plan
and this

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Agreement, including any liability and claim arising with regard to the
provisions of Article SECOND, unless such liability or claim results from
negligent, reckless or willful acts of commission or omission by the Trustee. To
the maximum extent permitted by ERISA and other applicable law, the Trustee
shall not be liable for acting (or for taking no action) in accordance with any
written direction of the Committee or an investment manager designated under
Article SECOND, or, where an investment manager has been designated, failing to
act in the absence of any such direction, including, without limitation, any
claim or liability that may be asserted against the Trustee on account of
failure to receive securities purchased, or failure to deliver securities sold
pursuant to orders issued by an investment manager, and the Company shall
indemnify the Trustee against and agrees to hold the Trustee harmless from, all
such liabilities and claims (including attorney's fees and expenses in defending
against such liabilities and claims). The foregoing indemnifications shall also
apply to liabilities and claims against the Trustee arising from any breach of
fiduciary responsibility by a fiduciary other than the Trustee, unless the
Trustee (i) participates knowingly in or knowingly undertakes to conceal such
breach, (ii) has enabled such fiduciary to commit such breach by its failure to
exercise its fiduciary duties under ERISA or (iii) has actual knowledge of such
breach and fails to take reasonable remedial action to remedy such breach.

     NINTH: Accounts. The Trustee or its agent shall keep records of all
transactions relating to the Trust Fund, which shall be made available at all
reasonable times to persons designated by the Board of Directors of the Company
or as may be required by law. The Trustee or its agent shall render an
accounting to the Company and the Committee at least annually which shall be in
a form sufficient to produce financial statements and to conduct an audit as
required by ERISA and the Code. The Committee may approve such accounting on
behalf of itself and the Company by an

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instrument in writing delivered to the Trustee. If the Committee does not file
with the Trustee objections to any such accounting within sixty (60) days after
its receipt, the Committee shall be deemed to have approved such accounting on
behalf of itself and the Company. In such case, or upon the written approval of
the Committee of any such accounting, the Trustee shall, to the extent permitted
by law, be discharged from all liability to the Committee and the Company for
its acts or failures to act described in such accounting. Except to the extent
otherwise provided in ERISA, no person, other than the Company or the Committee,
may require an accounting or bring any action against the Trustee with respect
to the Trust Fund. The Trustee shall render to the Committee, at least
quarterly, a statement of the Trust Fund assets and their values and, whenever a
contribution is made to the Trust Fund other than in cash, a statement of the
value of such property on the date it is received by the Trustee.

     Nothing contained in this Agreement or in the Plan shall deprive the
Trustee of the right to have judicial settlement of its accounts. In any
proceeding for a judicial settlement of the Trustee's accounts, or for
instructions with regard to the Trust, the only necessary parties thereto in
addition to the Trustee shall be the Committee. If the Trustee so elects, it may
join as a party or parties defendant any other person or persons.

     TENTH: Committee. The Company shall certify to the Trustee the names of the
persons from time to time constituting the Committee. All directions to the
Trustee by the Committee shall be in writing, and the Trustee shall be entitled
to rely without further inquiry upon all such written directions received from
the Committee.

     ELEVENTH: Compensation and Expenses. The Trustee shall be entitled to
receive such reasonable compensation for its services as may be agreed upon from
time to time by the Company

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and the Trustee. Unless paid by Company, such compensation, attorneys' fees
incurred in the administration of the Trust Fund, all taxes levied or assessed
against the Trust Fund, and such other expenses as are incurred in the
administration of the Trust Fund shall be paid from the Trust Fund.

     TWELFTH: Resignation of Trustee. The Trustee may resign at any time by
giving thirty (30) days written notice to the Company. The Board of Directors of
the Company may remove the Trustee at any time by giving thirty (30) days
written notice to the Trustee. In the case of the resignation or removal of the
Trustee, the Board of Directors of the Company shall appoint a successor trustee
who shall have the same powers and duties as those conferred upon the Trustee.
Upon the resignation or removal of the Trustee and the appointment of the
successor trustee, the Trustee shall account for the administration of the Trust
Fund up to the date of its resignation or removal in the manner provided in
Article NINTH hereof and, upon the approval or deemed approval of such
accounting, the Trustee shall transfer to the successor trustee all of the
assets then constituting the Trust Fund and the Trustee shall to the maximum
extent permitted by ERISA be forever released and discharged from all liability
and accountability with respect to the propriety of its acts and transactions;
provided, however, that the Trustee may, in its sole discretion, transfer such
assets prior to the completion of such accounting if the Company agrees thereto
in writing, such writing to include such limitations on the Trustee's liability
therefor as the Trustee may deem appropriate. The term "Trustee" as used in this
Agreement shall be deemed to apply to any successor trustee acting hereunder.

     THIRTEENTH: Amendment. The Board of Directors of the Company may amend all
or any part of this Agreement at any time provided, however, that any amendment
shall not be effective until the instrument of amendment has been agreed to and
executed by the Trustee. Any such

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amendment or modification of this Agreement may be retroactive if necessary or
appropriate to qualify or maintain the Trust Fund as a part of a plan and trust
exempt from federal income taxation under Sections 401(a) and 501(a) of the
Code, the provisions of ERISA, or any other applicable provisions of federal or
state law, as now in effect or hereafter amended or adopted, and any regulations
issued thereunder, including, without limitation, any regulations issued by the
United States Treasury Department, or the United States Department of Labor.

     Notwithstanding anything contained in this Article THIRTEENTH to the
contrary, no amendment shall divert any part of the Trust Fund to, and no part
of the Trust Fund shall be used for, any purpose other than for the exclusive
purpose of providing benefits to Participants and their beneficiaries; provided,
however, that nothing in this Article THIRTEENTH shall be deemed to limit or
otherwise prevent the payment from the Trust Fund of expenses and other charges
as provided in Article ELEVENTH.

     FOURTEENTH: Termination. This Agreement and the Trust Fund hereby created
may be terminated at any time by the Board of Directors of the Company by
written notice, executed and acknowledged so as to authorize it to be recorded
in the State of Missouri delivered to the Trustee. Upon receipt of such notice
of termination, the Trustee shall, after payment of all expenses incurred in the
administration of the Trust Fund and such compensation as the Trustee may be
entitled to, and upon approval of the appropriate governmental or
quasi-governmental authorities (if such approval shall be required under
applicable law or desired by the Trustee), then distribute the Trust Fund in
cash or in kind to such persons or entities, including the Company, at such time
and in such amounts as the Committee shall direct, which direction shall be in
conformity with the provisions of the Plan and ERISA.

                                       17
<PAGE>   20

     FIFTEENTH: Plan-to-Plan Transfers; Rollovers. The Trustee or its agent may
transfer all of the property representing a Participant's vested interest in the
Plan to the trustees of any trust qualified under Section 401(a) of the Code.
The Trustee or its agent may make such a transfer only at the direction of the
Committee.

     The Trustee may accept as part of the Trust Fund such property as is
acceptable to the Trustee that represents a Participant's retirement benefits
transferred from a trust qualified under Section 401(a) of the Code or
transferred from the Participant or an individual retirement account as a
permissible rollover under Section 402(c) or 408(d)(3) of the Code. The Trustee
may accept such a transfer only at the direction of the Committee. A Participant
shall at all times be fully vested in any property so transferred as a rollover
to the Trust Fund. Such property shall be distributed to the Participant or his
beneficiary at the direction of the Committee within the time required for
distribution of his or her retirement benefits under the applicable provisions
of the Plan.

     SIXTEENTH: Designation of Other Employers. The Committee may designate any
entity or organization eligible by law to participate in the Plan and the Trust
as a "Participating Employer" by written instrument delivered to the Secretary
of the Company, the Trustee and the designated Participating Employer. Such
written instrument shall specify the effective date of such designated
participation. Each designated Participating Employer shall become a party to
this Agreement and shall be conclusively presumed to have consented to its
designation and to have agreed to be bound by the terms of the Plan and this
Agreement and any and all amendments thereto upon its submission of information
to the Committee required by the terms of or with respect to the Plan or upon
making a contribution to the Trust Fund pursuant to the terms of the Plan. The
Company shall have the sole authority to enforce this Agreement on behalf of any
such Participating Employer and the Trustee

                                       18
<PAGE>   21

shall in no event be required to deal with any such Participating Employer
except by dealing with the Company as its agent. Irrespective of the number of
Participating Employers which may become parties to this Agreement, the Trustee
shall in all respects invest and administer the Trust Fund as a single fund for
investment and accounting purposes without allocation of any part of the Trust
Fund as between the Company and any such Participating Employer.

     Any Participating Employer may, by appropriate action of its Board of
Directors or noncorporate counterpart that is communicated in writing to the
Secretary of the Company, the Trustee and to the Committee, terminate its
participation in the Plan and the Trust. Moreover, the Committee may, in its
discretion, terminate an Employer's Plan and Trust participation at any time by
written instrument delivered to the Secretary of the Company, the Trustee and
the designated Employer. In such event, or in the event of the merger,
consolidation, sale of property or stock, separation, reorganization or
liquidation of the Company or of any such Participating Employer, or in the
event of the establishment, modification or continuance of any other retirement
plan that separately or in conjunction with this Plan qualifies under Section
401(a) of the Code, the Trustee shall continue to hold the portion of the Trust
Fund that is attributable to the participation in the Plan of the employees and
their beneficiaries affected by such termination or by such transaction, and
this Agreement shall continue in force with respect to such portion, until
otherwise directed by the Committee, in accordance with the provisions of the
Plan and ERISA.

     SEVENTEENTH: Alienation. No interest in the Trust Fund shall be assignable
or subject to anticipation, sale, transfer, mortgage, pledge, charge,
garnishment, attachment, bankruptcy or encumbrance or levy of any kind, and the
Trustee shall not recognize any attempt to assign, sell, transfer, mortgage,
pledge, charge, garnish, attach or otherwise encumber the same except to the

                                       19
<PAGE>   22

extent that such attempt is made pursuant to a court order determined by the
plan administrator to be a qualified domestic relations order or judgment or
settlement described in Section 401(a)(13) or Section 414(p) of the Code and
Section 206 of ERISA, or as otherwise required by law.

     EIGHTEENTH: Bond. The Trustee shall not be required to give any bond or any
other security for the faithful performance of its duties under this Agreement
except as required by law.

     NINETEENTH: Successors. This Agreement shall be binding upon the respective
successors and assigns of the Company and the Trustee. Any corporation that
shall, by merger, consolidation, purchase or otherwise, succeed to substantially
all the trust business of the Trustee shall, upon such succession, and without
any appointment or other action by any person, be and become successor Trustee
hereunder.

     TWENTIETH: Severability. If any provision of this Agreement is held to be
invalid, such invalidity shall not affect the remaining provisions of the
Agreement and they shall be construed and enforced as if such invalid provisions
had never been inserted therein.

     TWENTY-FIRST: Communications. Communications to the Company or the
Committee shall be addressed to:

                                      NATCO
                             BROOKHOLLOW CENTRAL III
                              2950 NORTH LOOP WEST
                                    SUITE 700
                                HOUSTON, TX 77092
             ATTENTION: A. L. SMITH, VICE PRESIDENT, HUMAN RESOURCES
                               (OR HIS SUCCESSOR)

                                       20
<PAGE>   23

provided, however, that upon the Company's written request such communications
shall be sent to such other address as the Company may specify.

     Communications to the Trustee shall be addressed to:

                                 UMB BANK, N.A.
                            EMPLOYEE BENEFIT DIVISION
                                1010 GRAND AVENUE
                                 P.O. BOX 419692
                           KANSAS CITY, MO 64141-6692

provided, however, that upon the Trustee's written request, such communications
shall be sent to such other address as the Trustee may specify. No communication
shall be binding on the Trustee until it is received by the Trustee.

     TWENTY-SECOND: Governing Law. This Agreement shall be construed in
accordance with ERISA and, to the extent not preempted by ERISA, the laws of the
State of Missouri.

                                       21
<PAGE>   24

     IN WITNESS WHEREOF, the Company and the Trustee have executed this
instrument this _______ day of _____________ , 199__.

                                             NATIONAL TANK COMPANY
ATTEST:

                                             By:
-----------------------------                   --------------------------------
Title:                                       Title:

(Corporate Seal)

                                             UMB BANK, N.A.

                                             By:
                                                --------------------------------
                                             Title:

                                       22

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