Wash. Rev. Code § 85.22.130
The board of county commissioners shall have all the powers possessed by the board of commissioners of any district reorganized under the provisions of this chapter prior to such reorganization, to levy assessments for the payment of the interest on any other bonds of the district not then payable and refunded under the provisions of this chapter, and to levy assessments to provide a sinking fund for the liquidation of such bonds at their maturity. Such assessments shall be called and collected in the manner provided by the law under which they were assessed, and such bonds shall be paid as provided by the law under which they were issued. Proper funds shall be established in the county treasury for the proceeds of the payments of such assessments, and such funds shall be applied to the payment of the bonds for the payment of which they were levied.
RCW 85.22.130