Wash. Rev. Code § 35.45.080
If a city or town fails to pay any bonds or to promptly collect any local improvement assessments when due, the owner of the bonds may proceed in his or her own name to collect the assessment and foreclose the lien thereof in any court of competent jurisdiction and shall recover in addition to the amount of the bond and interest thereon, five percent, together with the cost of suit. Any number of holders of bonds for any single improvement may join as plaintiffs and any number of owners of property upon which the assessments are liens may be joined as defendants in the same suit.
The owners of local improvement bonds issued by a city or town after the creation of a local improvement guaranty fund therein, shall also have recourse against the local improvement guaranty fund of such city or town unless the ordinance under which the bonds were issued provides that the bonds are not secured by the local improvement guaranty fund.
RCW 35.45.080