SIXTH CONSENT AND WAIVER UNDER THE SENIOR UNSECURED TERM LOAN AGREEMENT

Exhibit 4.2

SIXTH CONSENT AND WAIVER UNDER THE SENIOR UNSECURED

TERM LOAN AGREEMENT

Dated as of April 14, 2006

SIXTH CONSENT AND WAIVER UNDER THE SENIOR UNSECURED TERM LOAN AGREEMENT, dated as of April 14, 2006 (this “Consent”), among DRESSER, INC., a Delaware corporation (the “Borrower”), the Guarantors (as defined below), the Lenders listed on the signature pages hereto and MORGAN STANLEY SENIOR FUNDING, INC. (“MSSF”), as Administrative Agent.

W I T N E S S E T H:

WHEREAS, the Borrower, the Guarantors, the Lenders party thereto and the Agents have entered into a Senior Unsecured Term Loan Agreement dated as of March 1, 2004, as modified by the Consent and Waiver dated as of March 18, 2005, the Second Consent and Waiver dated as of May 27, 2005, the Third Consent and Waiver dated as of July 14, 2005, the Fourth Consent and Waiver dated as of September 29, 2005 and the Fifth Consent and Waiver dated as of November 14, 2005 (the “Term Loan Agreement”; capitalized terms used herein but not defined shall be used herein as defined in the Term Loan Agreement).

WHEREAS, the Borrower desires to modify the Term Loan Agreement in certain respects and to waive certain Defaults and Events of Default under the Term Loan Agreement, in each case as provided herein;

WHEREAS, the Required Lenders have agreed, subject to the terms and conditions hereinafter set forth, to modify the Term Loan Agreement in response to the Borrower’s request as set forth below;

NOW, THEREFORE, in consideration of the premises and for other good and valuable consideration (the receipt and sufficiency of which is hereby acknowledged), the parties hereto hereby agree as follows:

SECTION 1. Consent. Notwithstanding anything to the contrary set forth in the Term Loan Agreement, the Required Lenders hereby consent to (a) the extension of the delivery date specified for the audited financial statements for the Fiscal Year ended December 31, 2005 and the other material with respect to such Fiscal Year required by Section 5.01(b) of the Term Loan Agreement to no later than September 30, 2006 (the “10K Extended Delivery Date”), it being understood and agreed that if the Borrower fails to deliver such audited financial statements and other materials on or before the 10K Extended Delivery Date, and a notice of Default with respect to such failure is delivered to the Borrower by the Administrative Agent or the Lenders holding of at least 25% of the outstanding principal amount of the Senior Unsecured Obligations pursuant to Section 6.01(c) of the Term Loan Agreement, such failure shall constitute an Event of Default for all purposes under the Loan Documents and (b) the extension of the delivery date specified for the material required by Section 5.01(b) with respect to each of

the fiscal quarters ended March 31, 2006 and June 30, 2006 to no later than September 30, 2006 and any information required to be provided on a current report that is based on or derivative of such material, including any report that requires pro forma financial statements (the “10Q and 8K Extended Delivery Date”), it being understood and agreed that if the Borrower fails to deliver the materials required by Section 5.01(b) with respect to each of the fiscal quarters ended March 31, 2006 and June 30, 2006 by the 10Q and 8K Extended Delivery Date, and a notice of Default with respect to such failure is delivered to the Borrower by the Administrative Agent or the Lenders holding of at least 25% of the outstanding principal amount of the Senior Unsecured Obligations pursuant to Section 6.01(c) of the Term Loan Agreement, such failure shall constitute an Event of Default for all purposes under the Loan Documents. Notwithstanding the foregoing, it is further understood and agreed that the Borrower shall deliver to the Lenders all financial statements for each of the fiscal quarters ended March 31, 2006 and June 30, 2006 required to be delivered pursuant to Section 5.01(b) of the Term Loan Agreement at the same time as such financial statements are delivered to the “Lenders” under the Existing Credit Agreement, and if the Borrower fails to do so, and a notice of Default with respect to such failure is delivered to the Borrower by the Administrative Agent or the Lenders holding of at least 25% of the outstanding principal amount of the Senior Unsecured Obligations pursuant to Section 6.01(c) of the Term Loan Agreement, such failure shall constitute an Event of Default for all purposes under the Loan Documents.

SECTION 2. Waiver. The Lenders holding not less than a majority in aggregate principal amount of the then outstanding Senior Unsecured Obligations hereby waive any Default or Event of Default in respect of the provisions of Sections 3.01(a)(iv), 3.01(c), 4.01(f), 4.01(g), 4.01(h), 5.01(b) and 5.01(c) of the Term Loan 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 Consent and Waiver by the Borrower or any of its Subsidiaries (including, without limitation, any misstatement therein or in any certificate, representation or warranty relating thereto, or any error, defect or deficiency in accounting procedures or in the application of accounting principles reflected thereby or relating thereto), (ii) any failure to deliver any financial statement specified in Section 1 above when or as required, except as required by Section 1 above, (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.

SECTION 3. Conditions to Effectiveness. This Consent shall become effective as of the first date set forth above when each of the conditions set forth in this Section 3 to this Consent shall have been fulfilled to the satisfaction of the Administrative Agent.

(i) Execution of Counterparts. The Administrative Agent shall have received counterparts of this Consent, duly executed and delivered on behalf of each of (a) the Borrower and each Guarantor, (b) the Administrative Agent and (c) the Required Lenders, or as to any of the foregoing parties, advice reasonably satisfactory to the Administrative Agent that each of the foregoing parties has executed a counterpart of this Consent.

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(ii) Payment of Fees and Expenses. The Borrower shall have paid (a) to the Administrative Agent, for the benefit of each Lender executing this Consent on or before April 13, 2006, a fee equal to 0.10% of the aggregate Commitments and Advances of each such Lender and (b) all expenses (including the fees and expenses of Shearman & Sterling LLP) incurred in connection with the preparation, negotiation and execution of this Consent and other matters relating to the Term Loan Agreement from and after the last invoice to the extent invoiced.

The Administrative Agent will notify the Borrower when this Consent has become effective as set forth above, and such notice shall be conclusive and binding upon the Lenders.

SECTION 4. Representations and Warranties. Each Borrower hereby represents and warrants that, as of the date hereof and after giving effect to this Consent, no Default has occurred and is continuing or would result from the effectiveness of this Consent.

SECTION 5. Reference to and Effect on the Transaction Documents. (a) On and after the effectiveness of this Consent, each reference in the Term Loan Agreement to “hereunder”, “hereof” or words of like import referring to the Term Loan Agreement, and each reference in the other transaction documents to the “Credit Agreement”, “thereunder”, “thereof” or words of like import referring to the Term Loan Agreement, shall mean and be a reference to the Term Loan Agreement as modified by this Consent.

(b) The Term Loan Agreement, the Notes and each of the other Loan Documents, as specifically amended by this Consent, are and shall continue to be in full force and effect and are hereby in all respects ratified and confirmed.

(c) The execution, delivery and effectiveness of this Consent shall not, except as expressly provided herein, operate as a waiver of any right, power or remedy of any Lender or any 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 Consent 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 Consent by telecopier shall be effective as delivery of a manually executed counterpart of this Consent.

SECTION 7. Governing Law. This Consent shall be governed by, and construed in accordance with, the laws of the State of New York, and shall be subject to the jurisdictional and service provisions of the Term Loan Agreement, as if this were a part of the Term Loan Agreement.

SECTION 8. Entire Agreement; Modification. This Consent constitutes the entire agreement of the parties hereto with respect to the subject matter hereof, there being no other agreements or understandings, oral, written or otherwise, respecting such subject matter, any such agreement or understanding being superseded hereby, shall be binding upon and inure

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to the benefit of the parties hereto and their respective successors and assigns, and may not be amended, extended or otherwise modified, except in a writing executed in whole or in counterparts by each party hereto.

[Signatures follow.]

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

CONFIDENTIAL-FOR FRDG USE ONLY

CONFIDENTIAL-FOR FRDG USE ONLY

CONFIDENTIAL-FOR FRDG USE ONLY

CONFIDENTIAL-FOR FRDG USE ONLY

CONFIDENTIAL-FOR FRDG USE ONLY

CONFIDENTIAL-FOR FRDG USE ONLY

LENDERS

LENDERS