Wash. Rev. Code § 7.28.080
Every person having color of title made in good faith to vacant and unoccupied land, who shall pay all taxes legally assessed thereon for seven successive years, he or she shall be deemed and adjudged to be the legal owner of said vacant and unoccupied land to the extent and according to the purport of his or her paper title. All persons holding under such taxpayer, by purchase, devise or descent, before said seven years shall have expired, and who shall continue to pay the taxes as aforesaid, so as to complete the payment of said taxes for the term aforesaid, shall be entitled to the benefit of this section: PROVIDED, HOWEVER, If any person having a better paper title to said vacant and unoccupied land shall, during the said term of seven years, pay the taxes as assessed on said land for any one or more years of said term of seven years, then and in that case such taxpayer, his heirs or assigns, shall not be entitled to the benefit of this section.
RCW 7.28.080