Wash. Rev. Code § 35.44.280
In all cases of special assessments for local improvements wherein the assessments are not valid in whole or in part for want of form, or insufficiency, informality, irregularity, or nonconformance with the provisions of law, charter, or ordinance, the city or town council may reassess the assessments and enforce their collection in accordance with the provisions of law and ordinance existing at the time the reassessment is made. This shall apply not only to an original assessment but also to any reassessment, to any assessment upon omitted property and to any supplemental assessment which is declared void and its enforcement refused by any court or which for any cause has been set aside, annulled or declared void by any court either directly or by virtue of any decision thereof.
RCW 35.44.280