Wash. Rev. Code § 84.64.190
Whenever it shall be necessary in any action in any court of law or equity, wherein the title to any real property is in controversy, to prove the conveyance to any county of such real property in pursuance of a foreclosure of a tax certificate and sale thereunder, a copy of the tax deed issued to the county containing a description of such real property, exclusive of the description of all other real property therein described, certified by the county auditor of the county wherein the real property is situated, to be such, shall be admitted in evidence by the court, and shall be proof of the conveyance of the real property in controversy to such county, to the same extent as would a certified copy of the entire record of such tax deed.
RCW 84.64.190