Wash. Rev. Code § 15.65.440
Any due and payable assessment herein levied in such specified amount as may be determined by the director or his or her designee pursuant to the provisions of this chapter and such agreement or order, shall constitute a personal debt of every person so assessed or who otherwise owes the same, and the same shall be due and payable to the director or his or her designee when payment is called for by him or her. In the event any person fails to pay the director or his or her designee the full amount of such assessment or such other sum on or before the date due, the director or his or her designee may, and is hereby authorized to, add to such unpaid assessment or sum an amount not exceeding ten percent of the same to defray the cost of enforcing the collecting of the same. In the event of failure of such person or persons to pay any such due and payable assessment or other such sum, the director or his or her designee may bring a civil action against such person or persons in a court of competent jurisdiction for the collection thereof, together with the above specified ten percent thereon, and such action shall be tried and judgment rendered as in any other cause of action for debt due and payable.
RCW 15.65.440