Wash. Rev. Code § 39.53.080
When a public body has irrevocably set aside for and pledged to the payment of revenue bonds to be refunded refunding bond proceeds and other moneys in amounts which together with known earned income from the investment thereof are sufficient in amount to pay the principal of and interest and any redemption premiums on such revenue bonds as the same become due and to accomplish the refunding as scheduled, the governing body may provide that the refunding revenue bonds shall be payable from any source which, either at the time of the issuance of the refunding bonds or the revenue bonds to be refunded, might legally be or have been pledged for the payment of the revenue bonds to be refunded to the extent it may legally do so, notwithstanding the pledge of such revenues for the payment of the revenue bonds to be refunded.
RCW 39.53.080
Application-Construction-Severability-1999 c 230: See notes following RCW 39.53.010.