Wash. Rev. Code § 81.28.220
The attorney general of the state of Washington shall, whenever he or she has reasonable grounds to believe that any person, firm, or corporation has knowingly accepted or received from any carriers of persons or property subject to the jurisdiction of the commission, either directly or indirectly, any unlawful rebate, discount, deduction, concession, refund, or remittance from the rates or charges filed and open to public inspection as provided for in the public service laws of this state, prosecute a civil action in the name of the people of the state of Washington in the superior court of Thurston county to collect three times the total sum of such rebates, discounts, deductions, concessions, refunds, or remittances so accepted or received within three years prior to the commencement of such action.
All penalties imposed under the provisions of this section shall be paid to the state treasurer and by him or her deposited in the public service revolving fund.
RCW 81.28.220