Wash. Rev. Code § 91.08.280
Said 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 the law. Every commissioner shall receive compensation at the rate of five dollars per day for each day actually spent in making the assessment herein provided for, upon his or her filing in the proceeding a verified statement showing the number of days he or she has actually spent therein; and upon the approval of said statement by the judge of the court in which the proceeding is pending, the board shall issue a warrant in the amount so approved, upon the special fund created to pay the awards and costs of said proceeding; and the fees of such commissioners so paid, and all expenses returned by them and allowed by the court shall be included in the cost and expense of such proceeding.
RCW 91.08.280