Wash. Rev. Code § 43.33A.170
The state investment board is authorized to establish commingled trust funds in the state treasury for the implementation of specific investment programs for any combination of funds under its jurisdiction. At the discretion of the state investment board, the funds under the jurisdiction of the board may participate in the investments made by the board through state investment board commingled trust funds. The state investment board may establish accounts within any such commingled trust fund as necessary for the implementation of specific investment programs. The combining of moneys from funds located outside the state treasury with moneys from funds located within the state treasury for investment under this section shall not affect the nature, character, or purpose of a participating fund.
RCW 43.33A.170