Wash. Rev. Code § 85.32.150
Whenever lands, or lands with improvements thereon, lying outside of the existing territorial limits of such district are ultimately placed upon the assessment roll of such district in the manner provided by this chapter so that such lands are subject to maintenance benefits as provided, the owner of such land shall be deemed to be an elector within such district, and shall have the same right to participate in all district affairs and to vote upon all matters submitted to the electors of said district, including that of electing or becoming commissioners for the district, all in the manner provided for voting and elections under existing law pertaining to drainage districts. If such owner is a corporation, one of its duly constituted officers shall be deemed to have the right as an elector to vote on behalf of such corporation.
RCW 85.32.150