Wash. Rev. Code § 36.61.130
A county legislative authority may adopt an ordinance providing for a committee of itself, or an officer, to hear objections to the special assessment roll, act as a board of equalization, and make recommendations to the full county legislative authority, which need not hold a public hearing on the special assessment roll. The ordinance shall provide a process by which an appeal may be made in writing to the full county legislative authority by a person protesting his or her special assessment or annual special assessments as confirmed by the committee or officer. The full county legislative authority by resolution shall approve the special assessment roll, modify and approve the special assessment roll as a result of hearing objections, or reject the special assessment roll and return it to the committee or officer for further work and recommendations. No objection to the decision of the full county legislative authority approving the special assessment roll may be considered by a court unless an objection to the decision has been timely filed with the county legislative authority as provided in this section.
RCW 36.61.130