Wash. Rev. Code § 53.36.050
The county treasurer acting as port treasurer shall create a fund to be known as the "Port of . . . . . . Fund," into which shall be paid all money received by him or her from the collection of taxes in behalf of such port district, and shall also maintain such other special funds as may be created by the port commission into which shall be placed such moneys as the port commission may by its resolution direct. All such port funds shall be deposited with the county depositories under the same restrictions, contracts, and security as is provided by statute for county depositories and all interest collected on such port funds shall belong to such port district and shall be deposited to its credit in the proper port funds: PROVIDED, That any portion of such port moneys determined by the port commission to be in excess of the current needs of the port district may be invested by the county treasurer in accordance with RCW 36.29.020, 36.29.022, and chapter 39.59 RCW, and all interest collected thereon shall likewise belong to such port district and shall be deposited to its credit in the proper port funds.
RCW 53.36.050
County depositaries: Chapter 36.48 RCW.