Wash. Rev. Code § 36.33A.050
The legislative authority of the county may, from time to time, place moneys in the fund from any source lawfully available to it and may transfer equipment, materials, and supplies of any office or department to the equipment rental and revolving fund with or without charge consistent with RCW 43.09.210. Charges for the rental of equipment and for providing materials, supplies, and services to any county office or department shall be paid monthly into the fund. Proceeds received from other governmental agencies for similar charges and from the sale of equipment or other personal property owned by the equipment rental and revolving fund, which is no longer of any value to or needed by the county, shall be placed in the fund as received.
RCW 36.33A.050