Wash. Rev. Code § 85.08.490
The purchaser, upon the foreclosure of any certificate of delinquency for any assessment or installment thereof, shall acquire title to such property subject to the installments of the assessment not yet due at the date of the decree of foreclosure, and the complaint, decree of foreclosure, order of sale, sale, certificate of sale and deed shall so state.
The holder of any certificate of delinquency for general taxes may, before commencing any action to foreclose the lien of such certificate, pay in full all drainage or diking or sewerage improvement district assessments or any installment thereof due and outstanding against the whole or any portion of the property included in such certificate of delinquency and the amount of all assessments so paid together with interest at ten percent per annum thereon shall be included in the amount for which foreclosure may be had; or, if he or she elects to foreclose such certificate without paying such assessments in full, the purchaser at such foreclosure sale shall acquire title to such property subject to all such drainage or diking or sewerage improvement district assessments. Any property in any drainage or diking or sewerage improvement district sold under foreclosure for general taxes shall remain subject to the lien of all drainage and diking or sewerage improvement district assessments or installments thereof not yet due at the time of the decree of foreclosure and the complaint, decree of foreclosure, order of sale, sale, certificate of sale and deed shall so state.
RCW 85.08.490