Wash. Rev. Code § 35.13A.060
Whenever more than one city, in whole or in part, is included within a district, the city which has within its boundaries sixty percent or more of the area of the assessed valuation of the district (in this section referred to as the "principal city") may, with the approval of any other city containing part of such district, assume responsibility for operation and maintenance of the district's property, facilities and equipment within such other city and make and enforce such charges for operation, maintenance and retirement of indebtedness as may be reasonable under all the circumstances.
Any other city having less than sixty percent in area or assessed valuation of such district, within its boundaries may install facilities and create local improvement districts or otherwise finance the cost of installation of such facilities and if such facilities have been installed in accordance with reasonable standards fixed by the principal city, such other city may connect such facilities to the utility system of such district operated by the principal city upon providing for payment by the owners or occupants of properties served thereby, of such charges established by the principal city as may be reasonable under the circumstances.
RCW 35.13A.060
Part headings not law-1999 c 153: See note following RCW 57.04.050.