RCW 35.49.090: Payment by joint owner.

If any assessment for a local improvement, or an installment thereof, or judgment for either of them is paid, or a certificate of sale for either of them is redeemed by a joint owner of any of the property so assessed, he or she may, after demand and refusal, recover from his or her co-owners, by an action brought in superior court, the respective portions of the payment which each co-owner should bear. He or she shall have a lien upon the undivided interests of his or her co-owners from the date of the payment made by him or her and in the action shall recover interest at ten percent from the date of payment by him or her and the costs of the action in addition to the principal sum due him or her.