Wash. Rev. Code § 86.09.499
The treasurer of the county in which the land is situated shall conduct the sale of all lands situated therein and must collect in addition to the assessment due as shown on the delinquent list the costs and expenses of sale and interest at the rate of ten percent per annum from the date or dates of delinquency as hereinbefore provided. On the day fixed for the sale, or some subsequent day to which he or she may have postponed it, and between the hours of ten o'clock a.m. and three o'clock p.m., the county treasurer making the sale must commence the same, beginning at the head of the list, and continuing alphabetically, or in the numerical order of the parcels, lots, or blocks, until completed. He or she may postpone the day of commencing the sale, or the sale from day to day, by giving oral notice thereof at the time of the postponement, but the sale must be completed within three weeks from the first day fixed.
RCW 86.09.499