Wash. Rev. Code § 89.30.175
Whenever in the judgment of the reclamation district board a system of drainage for any lands included in the operation of any general improvement or divisional district therein will be of special benefit to the lands of the general improvement or divisional district as a whole, it shall pass a resolution to that effect and call a further meeting of the board to determine the question. Notice of said meeting shall be given by the secretary for the same length of time and in the same manner as required by law for the meeting of the commission to hear the petition for the organization of the reclamation district. At the time and place mentioned in the notice the board shall meet, hear such evidence as shall be presented, and fully determine the matter by resolution, which said resolution shall be final and conclusive upon all persons as to the benefit of said system of drainage to the lands in the district.
RCW 89.30.175