<PAGE>

                                                                    EXHIBIT 4(T)

         SEVENTH AMENDMENT dated as of October 16, 2001 (this "AMENDMENT"), to
the Amended and Restated Debtor in Possession Credit Agreement, initially dated
as of June 11, 2000, amended and restated as of July 19, 2000 (as amended,
supplemented or otherwise modified from time to time, the "Credit Agreement")
among SAFETY-KLEEN SERVICES, INC., a Delaware corporation (the "Borrower"), the
financial institutions or entities from time to time parties to this Agreement
(the "Lenders"), THE TORONTO-DOMINION BANK, HOUSTON AGENCY, as letter of credit
issuing bank (the "Issuing Lender"), TORONTO DOMINION (TEXAS), INC., as
administrative agent (the "General Administrative Agent"), and THE CIT
GROUP/BUSINESS CREDIT, INC. ("CIT"), as collateral agent and underwriter (the
"Collateral Agent"; collectively with the General Administrative Agent, the
"Underwriters").

                                  WITNESSETH:

         WHEREAS, the Borrower has requested that the General Administrative
Agent and the Lenders agree to amend certain provisions of the Credit Agreement
upon the terms and subject to the conditions set forth herein; and

         WHEREAS, the General Administrative Agent and the Lenders have agreed
to such amendments only upon the terms and subject to the conditions set forth
herein.

         NOW, THEREFORE, in consideration of the premises and the mutual
covenants contained herein and in the Credit Agreement, the parties hereto
hereby agree as follows:

         1.       Defined Terms.  Unless otherwise defined herein, all
capitalized terms used herein shall have the meanings given to them in the
Credit Agreement.

         2.       Amendment of Section 3.1.  Section 3.1 of the Credit
Agreement is hereby amended by replacing Section 3.1(a) in its entirety with
the following new Section 3.1(a):

                           "(a) Subject to the terms and conditions hereof, the
         Issuing Lender, in reliance on the agreements of the L/C Lenders set
         forth in Section 3.4(a), agrees to issue letters of credit (the
         "Letters of Credit") for the account of the Borrower on any Business
         Day during the Commitment Period in such form as may be approved from
         time to time by the Issuing Lender; provided that the Issuing Lender
         shall have no obligation to provide any Letter of Credit if, after
         giving effect thereto, (i) the aggregate amount of the L/C Obligations
         then outstanding would exceed $95,000,000; (ii) the aggregate
         Extensions of Credit of all of the Lenders would exceed the lesser of
         (x) the aggregate Revolving Credit Commitments then in effect or (y)
         the Borrowing Base then in effect and provided, further, that (i) up to
         $35,000,000 of Letters of Credit shall be available solely to backstop
         automobile, liability, workers' compensation and similar insurance
         programs; (ii) up to $15,000,000 of Letters of Credit shall be
         available solely for performance bonds on new bids by Borrower or its
         Subsidiaries in the United States, (iii) up to $30,000,000 of Letters
         of Credit shall be available solely to provide additional financial
         assurance as required for compliance with

<PAGE>
                                                                               2


         Environmental Law with respect to those facilities identified in
         Attachment K to the Consent Agreement and Final Order (CAFO) Between
         Certain Debtors and the United States Environmental Protection Agency,
         as Amended on May 16, 2001 and (iv) up to $15,000,000 of Letters of
         Credit shall be available solely to provide additional financial
         assurance as required for shoring up existing Indian Harbor policies.
         The Letters of Credit referenced in the immediately preceding clauses
         (iii) and (iv) are collectively referred to herein as "Environmental
         Letters of Credit". Each Letter of Credit shall (i) be denominated in
         U.S. dollars and (ii) expire no later than the date which is 60 days
         after the Maturity Date, provided, however, that Environmental Letters
         of Credit shall expire no later than the date which is 190 days after
         the Maturity Date."

         3.       Amendment of Section 7.11. Section 7.11 of the Credit
Agreement is hereby amended by replacing Section 7.11 in its entirety as
follows:

                           "7.11  Financial Condition Covenants. The General
         Administrative Agent and the Underwriters shall negotiate in good faith
         such financial covenants (including capital expenditure limitations) as
         they may deem appropriate in their sole discretion. On or before
         November 30, 2001, the Borrower shall execute and deliver to the
         General Administrative Agent an amendment in form and substance
         satisfactory to the General Administrative Agent and the Underwriters,
         containing the above-referenced financial covenants."

         4.       Amendment of Section 9(p). Section 9(p) of the Credit
Agreement is hereby amended by replacing Section 9(p) in its entirety as
follows:

                           "(p) the Borrower shall have failed to deliver to the
         Underwriters, by January 31, 2002, a preliminary Plan of
         Reorganization;"

         5.       Representations and Warranties. After giving effect to this
Amendment, the Borrower hereby represents and warrants that all of the
representations and warranties contained in the Credit Agreement are true and
correct in all material respects as of the date hereof (unless stated to relate
to a specific earlier date, in which case such representations and warranties
shall be true and correct in all material respects as of such earlier date) and
that no Default or Event of Default has occurred and is continuing.

         6.       Expenses. The Borrower agrees to pay and reimburse the General
Administrative Agent for all of its reasonable out-of-pocket costs and expenses
incurred in connection with the negotiation, preparation, execution, and
delivery of this Amendment, including the reasonable fees and expenses of
counsel.

         7.       Effectiveness. This Amendment shall become effective on the
date upon which the General Administrative Agent shall have received
counterparts hereof duly executed by the Borrower and the Required Lenders.
<PAGE>
                                                                             3


         8.       Continuing Effects.  Except as expressly waived or amended
hereby, the Credit Agreement shall continue to be and shall remain in full
force and effect in accordance with its terms.

         9.       Counterparts.  This Amendment may be executed by the parties
hereto on one or more counterparts, and all of such counterparts shall be
deemed to constitute one and the same instrument. This Amendment may be
delivered by facsimile transmission of the relevant signature pages hereof.

         10.      GOVERNING LAW.  THIS AMENDMENT SHALL BE GOVERNED BY, AND
CONSTRUED AND INTERPRETED IN ACCORDANCE WITH, THE LAW OF THE STATE OF NEW YORK.
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to
be duly executed and delivered by their proper and duly authorized officers as
of the day and year first above written.



                                       SAFETY-KLEEN SERVICES, INC.



                                       By: /s/ Larry W. Singleton
                                          --------------------------------------
                                          Name: LARRY W. SINGLETON
                                          Title: C.F.O.
                                          10-16-2001
<PAGE>
                                  TORONTO DOMINION (TEXAS), INC.,
                                    as General Administrative Agent, Underwriter
                                    and Lender



                                  By: /s/ Jano Nixon
                                     -------------------------------------------
                                     Name: JANO NIXON
                                     Title: VICE PRESIDENT



                                  THE TORONTO-DOMINION BANK,
                                  HOUSTON AGENCY
                                    as Issuing Lender



                                  By: /s/ Jano Nixon
                                     -------------------------------------------
                                     Name: Jano Nixon
                                     Title: Mgr. Syndications & Credit Admin.
<PAGE>

                                    THE CIT GROUP/BUSINESS CREDIT, INC.,
                                    as Collateral Agent, Underwriter and Lender



                                    By: /s/ Mark J. Long
                                       -----------------------------------------
                                       Name: Mark J. Long
                                       Title: Vice President
<PAGE>

                                       GOLDMAN SACHS CREDIT PARTNERS, L.P.



                                       By: /s/ David Sabath
                                          --------------------------------------
                                          Name: David Sabath
                                          Title: Authorized Signatory
<PAGE>

                                       GSCP Recovery, Inc.



                                       By: /s/ Matthew Kaufman
                                          --------------------------------------
                                          Name: Matthew Kaufman
                                          Title: Managing Director
<PAGE>

                               By: GSC Recovery II GP, L.P.,
                                     its general partner

                                     By: GSC RII, LLC,
                                           its general partner

                                           By: GSCP (NJ) Holdings, L.P.,
                                                 its sole member

                                                 By: GSCP (NJ), Inc.,
                                                       its general partner



                               By: /s/ Matthew Kaufman
                                  ----------------------------------------------
                                  Name: Matthew Kaufman
                                  Title: Managing Director
<PAGE>

                                       BANK ONE, NA



                                       By: /s/ Richard Babcock
                                          --------------------------------------
                                          Name: Richard Babcock
                                          Title: First Vice President
<PAGE>

                                   SENIOR DEBT PORTFOLIO
                                   By Boston Management and Research, as Advisor



                                   By: /s/ Scott H. Page
                                      ------------------------------------------
                                      Name: Scott H. Page
                                      Title: Vice President