Wash. Rev. Code § 35.73.050
Whenever any expense or cost of work has been assessed the amount of such expense and cost shall become a lien upon said lands against which the same are so assessed and shall take precedence of all other liens, except general tax liens and special assessment liens theretofore assessed by the said city thereon and which may be foreclosed in accordance with law in the name of such city as plaintiff. And in any such proceeding if the court trying the same shall be satisfied that the work has been done or material furnished for the fill of such property, a recovery shall be permitted or charge enforced to the extent of the proper proportion of the value of the work or material which would be chargeable on such lot or land notwithstanding any informality, irregularity or defects in any of the proceedings of such municipal corporation or its officers.
RCW 35.73.050
Collection and foreclosure of local improvement district assessments: Chapters 35.49, 35.50 RCW.