Wash. Rev. Code § 8.12.520
All the assessments levied by any city under this chapter shall, from the date of the judgment confirming the assessment be a lien upon the real estate upon which the same may be imposed, and such lien shall continue until such assessments are paid; if any proceedings taken for the enforcement thereof, shall be held void or invalid, such city shall provide by ordinance for new proceedings and a new sale for the enforcement thereof in like manner as hereinbefore provided; and in addition to the remedy hereinbefore provided, any city may enforce such lien by civil action in any court of competent jurisdiction in like manner and with like effect as actions for the foreclosure of mortgage.
RCW 8.12.520
Foreclosure actions, real estate mortgages: Chapter 61.12 RCW.