Wash. Rev. Code § 85.18.160
The board of commissioners of any diking district proceeding under this chapter shall, on or before the first day of November of each year, make an estimate of the costs reasonably anticipated to be required for the effective functioning of such district during the ensuing year and until further revenue therefor can be made available, and cause its chair or secretary to certify the same on or before said date to the county auditor, and the amount so certified shall be levied by the regular taxing agencies against the base benefits to the lands and buildings within such district as shown by the then current complete roll of such properties and the determined benefits thereto as therefore certified to and filed with such county auditor by the commissioners of such district. When thus levied, the amount of assessment produced thereby shall be added by the general taxing authorities to the general taxes against said lands and collected therewith as a part thereof. If unpaid, any delinquencies in such assessments shall bear interest at the same rate and in the same manner as general taxes and they shall be included in and be made a part of any general tax foreclosure proceedings, according to the provisions of law with relation to such foreclosures. As assessment collections are made, the county treasurer shall credit the same to the funds of such district.
RCW 85.18.160