Wash. Rev. Code § 8.12.270
All commissioners, before entering upon their duties, shall take and subscribe an oath that they will faithfully perform the duties of the office to which they are appointed, and will to the best of their abilities make true and impartial assessments according to law. Every commissioner shall receive compensation at the rate of ten dollars per day for each day actually spent in making the assessment herein provided for: PROVIDED, That in any city of the first class the superior court of the county in which said city is situated may, by order duly entered in its record, fix the compensation of each commissioner in an amount in no case to exceed twenty-five dollars per day for each day actually spent in making the assessment herein provided for. Each commissioner shall file in the proceeding in which he or she has made such assessment his or her account, stating the number of days he or she has actually spent in said proceeding, and upon the approval of said account by the judge before whom the proceeding is pending, the comptroller or city clerk of such city shall issue a warrant in the amount approved by the judge upon the special fund created to pay the awards and costs of said proceeding, and the fees of such commissioner so paid shall be included in the cost and expense of such proceedings. In case such commissioners are, during the same period, or parts thereof, engaged in making assessments in different proceedings, in rendering their accounts they shall apportion them to the different proceedings in proportion to the amount of time, actually spent by them on the assessment in each proceeding.
RCW 8.12.270