Wash. Rev. Code § 16.67.130
Any due and payable assessment levied under the provisions of this chapter shall constitute a personal debt of every person so assessed or who otherwise owes the same and shall be due and payable on the fifteenth day of the month following the month the transaction occurred. In the event any such person fails to pay the full amount within such time, the commission shall add to such unpaid assessment an amount of ten percent of the unpaid assessment to defray the cost of collecting the same. In the event of failure of such person to pay such due and payable assessment, the commission may bring civil action against such person in a state court of competent jurisdiction for the collection thereof, together with the above specified ten percent thereon and any other additional necessary reasonable costs including attorneys' fees. Such action shall be tried and judgment rendered as in any other cause of action for debt due and payable.
RCW 16.67.130