Wash. Rev. Code § 89.08.185
The local governing body of any city or incorporated town within an existing district may approve by majority vote a petition to withdraw from the district. The petition shall be submitted to the district for its approval. If approved by the district, the petition shall be sent to the commission. The commission shall approve the petition and forward it to the secretary of state and the boundary of the district shall be adjusted accordingly. If the petition is not approved by the district, the district shall adopt a resolution specifying the reasons why the petition is not approved. The petition and the district's resolution shall be sent to the commission for its review. The commission shall approve or reject the petition based upon criteria it has adopted for the evaluation of petitions in dispute. If the commission approves the petition, it shall forward the petition to the secretary of state and the boundaries of the district shall be adjusted accordingly. The criteria used by the commission to evaluate petitions which are in dispute shall be adopted as rules by the commission under chapter 34.05 RCW, the administrative procedure act.
RCW 89.08.185