<PAGE>

                                                                    EXHIBIT 4.11

                       AMENDMENT NO. 6 AND WAIVER TO THE
                               CREDIT AGREEMENT

                                                     Dated as of August 5, 2003

   AMENDMENT NO. 6 AND WAIVER TO THE CREDIT AGREEMENT among DRESSER, INC., a
Delaware corporation (the "U.S. Borrower"), and D.I. LUXEMBOURG S.A.R.L., a
corporation organized and existing under the laws of Luxembourg (the "Euro
Borrower", and, collectively with the U.S. Borrower, the "Borrowers"), DEG
ACQUISITIONS, LLC, a limited liability company organized and existing under the
laws of Delaware ("DEG Acquisitions"), DRESSER HOLDINGS, INC., a Delaware
corporation ("Dresser Holdings"), the Subsidiary Guarantors party to the Credit
Agreement referred to below (the "Subsidiary Guarantors"), the banks, financial
institutions and other institutional lenders party to the Credit Agreement
referred to below (collectively, the "Lenders"), WELLS FARGO BANK TEXAS, N.A.,
as the swing line bank, MORGAN STANLEY & CO. INCORPORATED, as collateral agent
(the "Collateral Agent"), MORGAN STANLEY SENIOR FUNDING, INC., as
administrative agent (the "Administrative Agent") for the Lenders and CREDIT
SUISSE FIRST BOSTON, as syndication agent (the "Syndication Agent", and
together with the Collateral Agent and the Administrative Agent, the "Agents").

   PRELIMINARY STATEMENTS:

   (1) The Borrowers, DEG Acquisitions, the Subsidiary Guarantors, the Lenders
and the Agents have entered into a Credit Agreement dated as of April 10, 2001,
as amended by Amendment No. 1 thereto dated as of March 13, 2002, Amendment No.
2 thereto dated as of June 17, 2002, Amendment No. 3 thereto dated as of
December 11, 2002, Amendment No. 4 and Waiver thereto dated as of March 31,
2003 and Amendment No. 5 dated as of June 30, 2003 (such Credit Agreement, as
amended, supplemented or otherwise modified through the date hereof, the
"Credit Agreement"). Dresser Holdings has entered into an Assignment and
Assumption Agreement dated as of July 3, 2002 with DEG Acquisitions whereby
Dresser Holdings assumed the duties and liabilities of DEG Acquisitions under
the Credit Agreement and the Security Agreement. Capitalized terms not
otherwise defined in this Amendment No. 6 and Waiver have the same meanings as
specified in the Credit Agreement.

   (2) The Borrowers have requested that the Lenders amend (i) certain
provisions of the Credit Agreement and (ii) waive certain Defaults and Events
of Default under the Credit Agreement, in each case as provided herein.

   (3) The Lenders party hereto, constituting not less than the Required
Lenders are, on the terms and conditions stated below, willing to grant the
request of the Borrowers as hereinafter set forth.

   NOW, THEREFORE, for good and valuable consideration the sufficiency of which
is hereby acknowledged, and subject to the terms and conditions of this
Amendment No. 6 and Waiver, the parties agree as follows:

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement

<PAGE>

                                       2

   SECTION 1. The Amendment. Subject to the satisfaction of the conditions
precedent set forth in Section 3, the Credit Agreement is, effective as of the
date hereof, hereby amended as follows:

       (a) The following definitions are hereby added to Section 1.01 of the
   Credit Agreement in correct alphabetical order:

          ""Amendment No. 5 " means Amendment No. 5 to this Agreement dated as
       of June 30, 2003 among the Borrowers, DEG Acquisitions, the Subsidiary
       Guarantors, the Lenders party thereto and the Agents."

          ""Amendment No. 6 and Waiver " means Amendment No. 6 and Waiver to
       this Agreement dated as of August 5, 2003 among the Borrowers, DEG
       Acquisitions, the Subsidiary Guarantors, the Lenders party thereto and
       the Agents."

          ""Amendment No. 6 and Waiver Effective Date" has the meaning set
       forth in Section 3 of Amendment No. 6 and Waiver."

       (b) The definition of "EBITDA" is amended in full to read:

          ""EBITDA" means, in each case of the U.S. Borrower and each of its
       Subsidiaries, for any period, the sum (without duplication) of (a) Net
       Income, (b) to the extent Net Income has been reduced thereby, (i) all
       income taxes and foreign withholding taxes paid or accrued for such
       period, (ii) Interest Expense, (iii) Non-cash Charges less any non-cash
       items increasing Net Income for such period (other than normal accruals
       in the ordinary course of business), (iv) any cash charges resulting
       from the Transactions and the related financings that, in each case, are
       incurred prior to the six month anniversary of the Initial Extension of
       Credit, and (v) any non-capitalized transactions costs incurred in
       connection with actual, proposed or abandoned financings, acquisitions
       or divestitures, including, but not limited to, financing and
       refinancing fees and costs incurred in connection with the Transactions,
       all as determined in accordance with GAAP for such period, (c) an
       allowance for losses (including lost earnings and incremental costs)
       incurred by the U.S. Borrower during the second and third fiscal
       quarters of the Fiscal Year ended December 31, 2003 attributable to a
       labor dispute at the Waukesha plant commencing on or about May 1, 2003,
       as reasonably determined in good faith by the U.S. Borrower, in an
       aggregate amount for all such losses under this clause (c) not to exceed
       $13,000,000, and (d) (1) fees and expenses related to or resulting from
       the re-audit and restatement of financial statements of the U.S.
       Borrower and its Subsidiaries (including the fees of accountants, legal
       counsel and others engaged to perform services in connection therewith),
       (2) fees payable and expenses incurred in connection with Amendment No.
       4 and Waiver, Amendment No. 5 and Amendment No. 6 and Waiver, and (3)
       fees payable in an aggregate amount reasonably approved by the
       Administrative Agent and expenses incurred in connection with a consent
       solicitation relating to Section 4.03 of the Indenture under which the
       Senior Subordinated Debt was issued.

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement

<PAGE>

                                       3

       Notwithstanding the foregoing, for purposes of the periods specified
       below, Consolidated EBITDA of the U.S. Borrower and its Subsidiaries
       shall mean the amount specified below:

<TABLE>
<CAPTION>
                 Quarter Ending               Consolidated EBITDA
               ------------------             -------------------
               <S>                            <C>
               December 31, 2000 .........     U.S.$ 58,300,000

               March 31, 2001 ............     U.S.$ 54,900,000
               June 30, 2001 .............     U.S.$ 56,067,000
               September 30, 2001 ........     U.S.$ 58,920,000
               December 31, 2001 .........     U.S.$ 59,652,000

               March 31, 2002 ............     U.S.$ 43,691,000
               June 30, 2002 .............     U.S.$ 47,700,000
               September 30, 2002 ........     U.S.$ 46,900,000
               December 31, 2002 .........     U.S.$ 29,400,000

               March 31, 2003 ............     U.S.$ 38,332,000
</TABLE>

      (c) The definition of "Applicable Margin" is amended by deleting the last
   two sentences in their entirety and substituting therefor the following:

          "Notwithstanding anything herein to the contrary but subject to the
       immediately succeeding sentence, for all purposes of the Agreement, the
       Applicable Margin shall be at Level VI during the period beginning on
       January 1, 2003 and ending on the date that the conditions set forth in
       Section 5.01(p) are met, and thereafter shall be determined in
       accordance with this definition without giving effect to this sentence.
       For all purposes of the Agreement, the Applicable Margin in effect from
       time to time pursuant to any of the foregoing for each of the Eurodollar
       Rate Advances and the Base Rate Advances shall increase by (x) during
       the period of time beginning on the Amendment No. 4 and Waiver Effective
       Date and ending on the date immediately prior to the Amendment No. 6 and
       Waiver Effective Date, 0.50%; and (y) during the period of time
       beginning on the Amendment No. 6 and Waiver Effective Date through the
       end of the Suspension Period, 1.00%."

      (d) The definition of "Suspension Period" is amended in full to read as
   follows:

          ""Suspension Period" means the period of time beginning on the
       Amendment No. 4 and Waiver Effective Date and ending on the earlier of
       (i) December 15, 2003 and (ii) the date on which the Agents receive (x)
       the audited annual financial statements for the U.S. Borrower and its
       Subsidiaries for the Fiscal Year ended in 2002 and (y) the revised,
       audited financial statements for the U.S. Borrower and its Subsidiaries
       for the Fiscal Year ended in 2001, in each case, in accordance with the
       requirements set forth in Section 5.01(p)."

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement

<PAGE>

                                       4

      (e) Section 5.01 is amended by adding the following clause (p) at the end
   thereof:

          "(p) Prior to December 15, 2003, the U.S. Borrower shall furnish to
       the Agents and the Lender Parties revised, audited annual financial
       statements for the Fiscal Year ended in 2001 and audited annual
       financial statements for the Fiscal Year ended in 2002, in each case as
       required by Section 5.03(b)."

      (f) Section 5.02(n) of the Credit Agreement is amended by deleting the
   amount "$15,000,000" specified in clause (1) thereof and substituting
   therefor the amount "$35,000,000".

   SECTION 2. Waiver and Standstill. (a) Subject to Section 3 hereof, the
Required Lenders hereby waive any Default or Event of Default in respect of the
provisions of Sections 2.06(b)(ii) (but only in respect of equity proceeds in
an amount not greater than $10,000,000 used to finance an asset acquisition),
2.07(a), 2.08(c), 3.01(a)(vi), 3.01(c), 3.01(e), 3.01(i), 3.02, 4.01(g),
4.01(h), 4.01(i), 4.01(j), 4.01(q)(ii), 5.01(a), 5.01(g), 5.02(b)(ii)(F) and
(G), 5.02(f)(vii), (viii) and (ix), 5.02(g), 5.03(a), 5.03(b), 5.03(c),
5.03(d), 5.04(a) and 5.04(b) of the Credit Agreement and any related or
substantially comparable provision of any Loan Document, in each case
consisting of, resulting from or relating in any respect to (i) the re-audit,
revision or restatement of any financial statement delivered prior to the date
of this Amendment by the U.S. Borrower or any of its Subsidiaries (including,
without limitation, any misstatement therein or in any certificate,
representation or warranty relating thereto and any error, defect or deficiency
in accounting procedures or in the application of accounting principles
reflected thereby or relating thereto or the absence of audited financial
statements for any fiscal period prior to Fiscal Year 2001), (ii) any failure
to deliver any such financial statement when or as required, except as required
by Section 5.01(p), (iii) any failure to comply with any obligation that became
required to be performed or observed under any of such provisions by reason of
the occurrence of any such Default or Event of Default or (iv) any misstatement
as to the absence of any such Default or Event of Default.

   (b) Subject to Section 3 hereof, the Required Lenders waive any Default or
Event of Default now existing or hereafter arising under Section 6.01(e) of the
Credit Agreement resulting from a default under Section 4.03 of the Indenture
under which the Senior Subordinated Debt was issued; provided, however, that
the exercise by the Trustee or the requisite holders of Senior Subordinated
Notes of their right to give a notice of acceleration pursuant to Section 6.02
of such Indenture by reason of the existence of such default under Section 4.03
of the Indenture shall constitute an immediate Event of Default.

   SECTION 3. Conditions of Effectiveness. This Amendment No. 6 and Waiver
shall become effective as of the first date (the "Amendment No. 6 and Waiver
Effective Date") on which each of the following conditions precedents shall
have been satisfied:

      (a) The Administrative Agent shall have received counterparts of this
   Amendment No. 6 and Waiver executed by the Borrowers, DEG Acquisitions,
   Dresser Holdings and the Required Lenders or, as to any of the Lenders,
   advice satisfactory to the Administrative Agent that such Lender has
   executed this Amendment No. 6 and Waiver.

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement

<PAGE>

                                       5

      (b) All of the accrued fees and expenses of the Administrative Agent
   (including the accrued fees and expenses of counsel for the Administrative
   Agent) for which invoices shall have been submitted shall have been paid in
   full.

      (c) The Administrative Agent shall have received the consent attached
   hereto duly executed by each Guarantor and each Grantor.

      (d) The U.S. Borrower shall have paid to the Administrative Agent, for
   the benefit of the applicable Lenders, a fee equal to 0.25% of the aggregate
   Commitments of each Lender that has executed and delivered this Amendment
   No. 6 and Waiver on or before August 5, 2003.

   This Amendment No. 6 and Waiver is subject to the provisions of Section 9.01
of the Credit Agreement.

   SECTION 4. Representations and Warranties of the Borrower. Each Borrower
represents and warrants as follows:

      (a) On the date hereof, after giving effect to this Amendment No. 6 and
   Waiver, (i) no event has occurred and is continuing, or would result from
   the effectiveness of this Amendment No. 6 and Waiver, that constitutes a
   Default and (ii) all representations and warranties set forth in the Loan
   Documents shall be true and correct in all material respects.

      (b) No authorization or approval or other action by, and no notice to or
   filing with, any governmental authority or regulatory body or any other
   third party is required for the due execution, delivery or performance by
   the Borrowers of this Amendment No. 6 and Waiver and by the Guarantors and
   the Grantors of the consent attached hereto or other transactions
   contemplated hereby.

      (c) This Amendment No. 6 and Waiver has been duly executed and delivered
   by the Borrowers. The consent attached hereto has been duly executed and
   delivered by each of the Guarantors and the Grantors. This Amendment No. 6
   and Waiver and each of the other Loan Documents, as amended hereby, to which
   each Borrower, each Guarantor and each Grantor is a party are legal, valid
   and binding obligations of such Borrower, such Guarantor and such Grantor,
   as applicable, enforceable against such Borrower, such Guarantor and such
   Grantor, as applicable, in accordance with their respective terms.

   SECTION 5. Reference to and Effect on the Credit Agreement and the Notes.
(a) On and after the effectiveness of this Amendment No. 6 and Waiver, each
reference in the Credit Agreement to "this Agreement", "hereunder", "hereof" or
words of like import referring to the Credit Agreement, and each reference in
the Notes and each of the other Loan Documents to "the Credit Agreement",
"thereunder", "thereof" or words of like import referring to the Credit
Agreement, shall mean and be a reference to the Credit Agreement, as amended by
this Amendment No. 6 and Waiver.

   (b) The Credit Agreement, the Notes and each of the other Loan Documents, as
specifically amended by this Amendment No. 6 and Waiver, are and shall continue
to be in

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement

<PAGE>

                                       6

full force and effect and are hereby in all respects ratified and confirmed.
Without limiting the generality of the foregoing, the Collateral Documents and
all of the Collateral described therein do and shall continue to secure the
payment of all Obligations of the Loan Parties under the Loan Documents, in
each case as amended by this Amendment No. 6 and Waiver.

   (c) The execution, delivery and effectiveness of this Amendment No. 6 and
Waiver shall not, except as expressly provided herein, operate as a waiver of
any right, power or remedy of any Lender or the Administrative Agent under any
of the Loan Documents, nor constitute a waiver of any provision of any of the
Loan Documents.

   SECTION 6. Execution in Counterparts. This Amendment No. 6 and Waiver may be
executed in any number of counterparts and by different parties hereto in
separate counterparts, each of which when so executed shall be deemed to be an
original and all of which taken together shall constitute but one and the same
agreement. Delivery of an executed counterpart of a signature page to this
Amendment No. 6 and Waiver by telecopier shall be effective as delivery of a
manually executed counterpart of this Amendment No. 6 and Waiver.

   SECTION 7. Governing Law. This Amendment No. 6 and Waiver shall be governed
by, and construed in accordance with, the laws of the State of New York.

                     [SIGNATURE PAGES IMMEDIATELY FOLLOW]

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement

<PAGE>

   IN WITNESS WHEREOF, the parties hereto have caused this Amendment No. 6 and
Waiver to be executed by their respective officers thereunto duly authorized,
as of the date first above written.


                                              DRESSER, INC., as U.S. Borrower

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

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement

<PAGE>

                                            D.I. LUXEMBOURG S.A.R.L., as Euro
                                            Borrower

                                            By _______________________________
                                                Name:
                                                Title:

                       Amendment No. 6 and Waiver to the
                            Dresser Credit Agreement

<PAGE>

                                    DEG ACQUISITIONS, LLC

                                    By: FIRST RESERVE FUND VIII, L.P., a
                                        Delaware limited partnership, its
                                        Manager
                                        By: FIRST RESERVE GP VIII, L.P., a
                                            Delaware limited partnership, its
                                            general partner
                                            By: FIRST RESERVE CORPORATION, a
                                                Delaware corporation, its
                                                general partner

                                            By: ______________________________
                                                Name:
                                                Title:

                       Amendment No. 6 and Waiver to the
                            Dresser Credit Agreement

<PAGE>

                                            DRESSER HOLDINGS, INC.

                                            By _______________________________
                                                Name:
                                                Title:

                       Amendment No. 6 and Waiver to the
                            Dresser Credit Agreement

<PAGE>

                                            MORGAN STANLEY SENIOR FUNDING, INC.,
                                            as Administrative Agent

                                            By _______________________________
                                                Name:
                                                Title:

                       Amendment No. 6 and Waiver to the
                            Dresser Credit Agreement

<PAGE>

                                            MORGAN STANLEY & CO. INCORPORATED,
                                            as Collateral Agent

                                            By _______________________________
                                                Name:
                                                Title:

                       Amendment No. 6 and Waiver to the
                            Dresser Credit Agreement

<PAGE>

                                            CREDIT SUISSE FIRST BOSTON, as
                                            Syndication Agent

                                            By _______________________________
                                                Name:
                                                Title:

                                            By _______________________________
                                                Name:
                                                Title:

                       Amendment No. 6 and Waiver to the
                            Dresser Credit Agreement

<PAGE>

                                            GENERAL ELECTRIC CAPITAL
                                            CORPORATION, as Co-Documentation
                                            Agent

                                            By _______________________________
                                                Name:
                                                Title:

                       Amendment No. 6 and Waiver to the
                            Dresser Credit Agreement

<PAGE>

                                         REVOLVING CREDIT LENDERS, TRANCHEA
                                         EURO TERM LENDERS AND TRANCHE AU.S.
                                         TERM LENDERS

                                           _____________________________________
                                           [Print Name of Financial Institution]

                                             By ____________________________
                                                Name:
                                                Title:

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement

<PAGE>


                                         TRANCHE B TERM LENDERS
                                            ____________________________________
                                           [Print Name of Financial Institution]

                                             By ____________________________
                                                Name:
                                                Title:

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement

<PAGE>


                                         ISSUING BANKS

                                             WELLS FARGO BANK, N.A.

                                             By ____________________________
                                                Name:
                                                Title:

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement

<PAGE>


                                         CREDIT SUISSE FIRST BOSTON

                                             By ____________________________
                                                Name:
                                                Title:

                                             By ____________________________
                                                Name:
                                                Title:

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement

<PAGE>


                                         SWING LINE BANK

                                             WELLS FARGO BANK TEXAS, N.A.

                                             By ____________________________
                                                Name:
                                                Title:

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement

<PAGE>


                                    CONSENT

                                                      Dated as of August 5, 2003

   Each of the undersigned as a Loan Party under the Credit Agreement referred
to in the foregoing Amendment No. 6 and Waiver and as Grantor under the Security
Agreement dated as of April 10, 2001 (as amended, supplemented or otherwise
modified from time to time, the "Security Agreement") in favor of the Collateral
Agent, for its benefit and the benefit of the Lenders party to the Credit
Agreement referred to in the foregoing Amendment No. 6 and Waiver, hereby
consents to such Amendment No. 6 and Waiver and hereby confirms and agrees that
(a) notwithstanding the effectiveness of such Amendment No. 6 and Waiver, each
Loan Document is, and shall continue to be, in full force and effect and is
hereby ratified and confirmed in all respects, except that, on and after the
effectiveness of such Amendment No. 6 and Waiver, each reference in each Loan
Document to the "Credit Agreement", "thereunder", "thereof" or words of like
import shall mean and be a reference to the Credit Agreement, as amended by such
Amendment No. 6 and Waiver, and (b) the Collateral Documents to which such
Grantor is a party and all of the Collateral described therein do, and shall
continue to, secure the payment of all of the Secured Obligations (in each case,
as defined therein).

                                      DEG ACQUISITIONS, LLC

                                      By: FIRST RESERVE FUND VIII, L.P., a
                                          Delaware limited partnership, its
                                          Manager
                                          By: FIRST RESERVE GP VIII, L.P., a
                                              Delaware limited partnership,
                                              its general partner
                                              By: FIRST RESERVE CORPORATION,
                                                  a Delaware corporation, its
                                                  general partner

                                              By: ____________________________
                                                  Name:
                                                  Title:

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement

<PAGE>


                                         DRESSER HOLDINGS, INC.

                                             By ____________________________
                                                Name:
                                                Title:

                                         DRESSER INTERNATIONAL, INC.

                                             By ____________________________
                                                Name:
                                                Title:

                                         DRESSER RE, INC.

                                             By ____________________________
                                                Name:
                                                Title:

                                         DRESSER RUSSIA, INC.

                                             By ____________________________
                                                Name:
                                                Title:

                                         LVF HOLDING CORPORATION

                                             By ____________________________
                                                Name:
                                                Title:

                                         MODERN ACQUISITION, INC.

                                             By ____________________________
                                                Name:
                                                Title:

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement

<PAGE>


                                         DRESSER ENTECH, INC.

                                             By ____________________________
                                                Name:
                                                Title:

                                         RING-O VALVE, INCORPORATED

                                             By ____________________________
                                                Name:
                                                Title:

                       Amendment No. 6 and Waiver to the
                           Dresser Credit Agreement