Wash. Rev. Code § 91.08.540
During the construction of the improvement said board shall have the right to allow payment therefor to contractors in installments as the work progresses, in proportion to the amount of work completed: PROVIDED, That no such allowance or payment shall be made for exceeding seventy-five percent of the proportionate amount of the work completed; and twenty-five percent of the contract price shall be reserved at all times by said board until such work is fully completed, and shall not be paid until thirty days have expired after such completion. Upon completion of the work and the production of satisfactory evidence to the board that all just claims for labor, materials, goods, wares, merchandise and provisions furnished to the contractor have been paid, the board shall accept the improvement and pay the contract price therefor.
RCW 91.08.540