Wash. Rev. Code § 35.02.132
The newly elected officials shall adopt an interim budget for the interim period or until January 1 of the following year, whichever occurs first. A second interim budget shall be adopted for any period between January 1 and the official date of incorporation. These interim budgets shall be adopted in consultation with the state auditor.
The governing body shall adopt a budget for the newly incorporated city or town for the period between the official date of incorporation and January 1 of the following year. The mayor or governing body, whichever is appropriate shall prepare or the governing body may direct the interim city manager to prepare a preliminary budget in detail to be made public at least sixty days before the official date of incorporation as a recommendation for the final budget. The mayor, governing body, or the interim city manager shall submit as a part of the preliminary budget a budget message that contains an explanation of the budget document, an outline of the recommended financial policies and programs of the city or town for the ensuing fiscal year, and a statement of the relation of the recommended appropriation to such policies and programs. Immediately following the release of the preliminary budget, the governing body shall cause to be published a notice once each week for two consecutive weeks of a public hearing to be held at least twenty days before the official date of incorporation on the fixing of the final budget. Any taxpayer may appear and be heard for or against any part of the budget. The governing body may make such adjustments and changes as it deems necessary and may adopt the final budget at the conclusion of the public hearing or at any time before the official date of incorporation.
RCW 35.02.132