Wash. Rev. Code § 87.03.280
Where any district under contract with the United States has levied any assessment for the collection of money payable to the United States under such contract, and the secretary of the interior has by agreement with the board of directors of said district, authorized the extension or cancellation of any payments due to the United States by the cancellation of assessments already levied therefor but remaining unpaid, the board of directors of such district shall certify to the county treasurer of the county in which the land is located, a statement of the year and amounts assessed against each tract for which such cancellation has been authorized, and the county treasurer, upon receipt of such certificate, shall, in all cases where the assessment remains unpaid and the lands have not been sold, endorse upon the district's assessment roll, "Corrected under Certificate of Board of Directors" and shall deduct and cancel from the assessment against each such tract the amount of such assessment so authorized to be canceled; and in all cases where such cancellations have been certified to the county treasurer after such lands assessed have been sold and before the period of redemption shall have expired, the county treasurer shall, in those cases where the tract assessed has been sold to the district, and the district is the owner of the certificate of sale, require the district to surrender its certificate of sale and shall thereupon deduct the amount of such cancellation plus the penalties thereon upon the original assessment roll with an endorsement, "Corrected under Certificate of Board of Directors" and he or she shall thereupon issue to the district in lieu of the certificate surrendered, a substitute certificate of sale for the corrected amount of such assessment, if any, remaining uncanceled, and shall file a copy thereof in the office of the county auditor as in the case of the original certificate surrendered, and such substitute certificate shall entitle the holder thereof to all rights possessed under the original certificate so corrected as to amount: PROVIDED, HOWEVER, That such cancellation shall have the same effect as though the lands had originally not been assessed for the amounts so deducted and shall not operate to bar the district of the right in making subsequent annual assessments to levy and collect against such tracts the amount of any money due the United States, including the amount of any assessments so canceled.
RCW 87.03.280
Board's powers and duties (contracts with state and United States): RCW 87.03.140.