Wash. Rev. Code § 85.05.077
In all cases wherein it is finally determined that the assessments for the system of drainage differ from the assessment theretofore made, as to any tract or parcel of land within said diking district, the diking commissioners in making their annual estimate shall segregate the amount necessary to be raised for the construction, repair and maintenance of the system of drainage or for the payment of the principal or interest of any bonds issued for drainage purposes from the amount necessary to be raised for all other diking purposes and the county auditor in apportioning said estimate for drainage purposes to the lands in such district shall base such apportionment upon the assessment fixed for drainage purposes and shall apportion the remainder of such estimate upon the basis fixed in the original or any subsequent proceeding for all other diking purposes. But in all other cases, the estimate and apportionment shall be made in accordance with existing laws.
RCW 85.05.077