Wash. Rev. Code § 84.56.270
The county treasurer of any county of the state of Washington, after he or she has first received the approval of the board of county commissioners of such county, through a resolution duly adopted, is hereby empowered to petition the superior court in or for his or her county to finally cancel and completely extinguish the lien of any delinquent personal property tax which appears on the tax rolls of his or her county, which is more than four years delinquent, which he or she attests to be beyond hope of collection, and the cancellation of which will not impair the obligation of any bond issue nor be precluded by any other legal impediment that might invalidate such cancellation. The superior court shall have jurisdiction to hear any such petition and to enter such order as it shall deem proper in the premises.
RCW 84.56.270