Wash. Rev. Code § 36.35.240
The judgment rendered in such action, unless appealed from within the time prescribed herein and upon final judgment on appeal, shall be conclusive, without the right of redemption upon and against every person who may or could claim any lien or any right, title or interest in or to any of the properties involved in said action, including minors, insane persons, those convicted of crime, as well as those free from disability, and against those who may have at any time attempted to pay any tax on any of the properties, and against those in actual open and notorious possession of any of said properties.
Such judgment shall be conclusive as to those who appeal therefrom, except as to the particular property to which such appellant laid claim in the action and concerning which he or she appealed, and shall be conclusive as to those in possession of any property and who were not served except as to the property which such person is in the actual, open and notorious possession of, and in any case where it is asserted that the judgment was not conclusive because of such possession, the burden of showing such actual, open and notorious possession shall be on the one asserting such possession.
RCW 36.35.240