Wash. Rev. Code § 43.52.470
Except as provided in RCW 43.52.360, the validity of the organization of any joint operating agency can be questioned only by action instituted within six months from the date that the joint operating agency is created. If the validity of the existence of any joint operating agency is not challenged within that period, by the filing and service of a petition or complaint in the action, the state shall be barred forever from questioning the validity of the joint operating agency by reason of any defect claimed to exist in the organization thereof, and it shall be deemed validly organized for all purposes. Any joint operating agency heretofore (March 26, 1957) attempted to be organized pursuant to chapter 43.52 RCW and which has maintained its existence since the date of such attempted organization, is hereby declared legal and valid and its organization and creation are validated and confirmed.
RCW 43.52.470