Wash. Rev. Code § 35.50.030
If on the first day of January in any year, two installments of any local improvement assessment are delinquent, or if the final installment thereof has been delinquent for more than one year, the city or town shall proceed with the foreclosure of the delinquent assessment or delinquent installments thereof by proceedings brought in its own name in the superior court of the county in which the city or town is situate.
The proceedings shall be commenced on or before March 1st of that year or on or before such other date in such year as may be fixed by general ordinance, but not before the city or town treasurer has notified by certified mail the persons whose names appear on the current assessment roll as owners of the property charged with the assessments or installments which are delinquent, at the address last known to the treasurer, a notice thirty days before the commencement of the proceedings. If the person whose name appears on the assessment rolls of the county assessor as owner of the property, or whose name appears on the tax rolls of the county treasurer as taxpayer of the property, or the address shown for the owner, differs from that appearing on the city or town assessment roll, then the treasurer shall also mail a copy of the notice to that person or that address.
The notice shall state the amount due, including foreclosure costs, upon each separate lot, tract, or parcel of land and the date after which the proceedings will be commenced. The city or town treasurer shall file with the clerk of the superior court at the time of commencement of the foreclosure proceeding the affidavit of the person who mailed the notices. This affidavit shall be conclusive proof of compliance with the requirements of this section.
RCW 35.50.030
Severability-1982 c 91: "If any provision of this amendatory act or its application to any person or circumstance is held invalid, the remainder of the act or the application of the provision to other persons or circumstances is not affected." [ 1982 c 91 s 10.]
Construction-1933 c 9: "The provisions of this act shall be applicable to the lien of assessments heretofore as well as hereafter levied and to foreclosure proceedings now pending." [ 1933 c 9 s 3.]