Wash. Rev. Code § 35.40.030
If, in any case where any city or town in this state has been or may hereafter be formed by the consolidation of two or more cities or towns, or has annexed or may hereafter annex any new territory, an election shall be held, in accordance with the Constitution and laws of this state, for the purpose of submitting to the voters residing within the former corporate limits of either such former city or town, or of such city or town prior to such annexation, for ratification or disapproval, the attempted incurring on the part of such former city or town or of such city or town prior to such annexation by the corporate authorities thereof, of any indebtedness thereof, such consolidated or existing city or town may submit to all of the voters therein, at the same or a separate election, any proposition to fund such indebtedness so sought to be ratified or any part thereof or any existing indebtedness of such consolidated or existing city or town, or both. The proposition to ratify any such indebtedness so previously attempted to be incurred on the part of either such former city or town, or on the part of such city or town prior to such annexation, and the proposition to fund the same may be submitted, respectively, to the voters residing within the corporate limits of such former city or town or in such city or town prior to such annexation, and to all the voters in such consolidated city or town, respectively, in the same or in separate ordinances, as may be required or permitted by law; but the proposition to fund shall be the subject of a distinct vote in favor of or against the same, separate from the vote upon the proposition to ratify, and separate from the vote upon a proposition to fund any part of such indebtedness as to which a proposition to ratify is not submitted.
RCW 35.40.030
Annexation of unincorporated areas: Chapter 35.13 RCW.
Consolidation including annexation of third-class city or town to first-class city: Chapter 35.10 RCW.