Wash. Rev. Code § 84.68.030
In case it be determined in such action that said tax, or any portion thereof, so paid under protest, was unlawfully collected, judgment for recovery thereof and interest thereon at the rate specified in RCW 84.69.100 from date of payment, together with costs of suit, shall be entered in favor of plaintiff. In case the action is against a county and the judgment shall become final, the amount of such judgment, including interest at the rate specified in RCW 84.69.100 and costs where allowed, shall be paid out of the treasury of such county by the county treasurer upon warrants drawn by the county auditor against a fund in said treasury hereby created to be known and designated as the county tax refund fund. Such warrants shall be so issued upon the filing with the county auditor and the county treasurer of duly authenticated copies of such judgment, and shall be paid by the county treasurer out of any moneys on hand in said fund. If no funds are available in such county tax refund fund for the payment of such warrants, then such warrants shall bear interest in such cases and shall be callable under such conditions as are provided by law for county warrants, and such interest, if any, shall also be paid out of said fund.
RCW 84.68.030