Wash. Rev. Code § 35.13.015
In addition to the method prescribed by RCW 35.13.020 for the commencement of annexation proceedings, the legislative body of any city or town may, whenever it shall determine by resolution that the best interests and general welfare of such city or town would be served by the annexation of unincorporated territory contiguous to such city or town, file a certified copy of the resolution with the board of county commissioners of the county in which said territory is located. The resolution of the city or town initiating such election shall, subject to RCW 35.02.170, describe the boundaries of the area to be annexed, as nearly as may be state the number of voters residing therein, pray for the calling of an election to be held among the qualified voters therein upon the question of annexation, and provide that said city or town will pay the cost of the annexation election. The resolution may require that there also be submitted to the electorate of the territory sought to be annexed a proposition that all property within the area annexed shall, upon annexation, be assessed and taxed at the same rate and on the same basis as the property of such annexing city or town is assessed and taxed to pay for all or any portion of the then outstanding indebtedness of the city or town to which said area is annexed, approved by the voters, contracted, or incurred prior to, or existing at, the date of annexation. Whenever a city or town has prepared and filed a comprehensive plan for the area to be annexed as provided for in RCW 35.13.177 and 35.13.178, the resolution initiating the election may also provide for the simultaneous adoption of the comprehensive plan upon approval of annexation by the electorate of the area to be annexed.
RCW 35.13.015
Legislative finding, intent-1975 1st ex.s. c 220: See note following RCW 35.02.170.