Wash. Rev. Code § 39.84.130
No part of the proceeds received from the sale of any revenue bonds under this chapter, of any revenues derived from any industrial development facility acquired or held under this chapter, or of any interest realized on moneys received under this chapter may be commingled by the public corporation with funds of the municipality creating the public corporation. However, those funds of the public corporation, other than proceeds received from the sale of revenue bonds, that are not otherwise encumbered for the payment of revenue bonds and are not reasonably anticipated by the board of directors to be necessary for administrative expenses of the public corporation may be transferred to the creating municipality and used for growth management, planning, or other economic development purposes.
RCW 39.84.130