Wash. Rev. Code § 84.56.330
Any person who has a lien by mortgage or otherwise, upon any real property upon which any taxes have not been paid, may pay such taxes, and the interest, penalty and costs thereon; and the receipt of the county treasurer or other collecting official shall constitute an additional lien upon such land, to the amount therein stated, and the amount so paid and the interest thereon at the rate specified in the mortgage or other instrument shall be collectible with, or as a part of, and in the same manner as the amount secured by the original lien: PROVIDED, That the person paying such taxes shall pay the same as mortgagee or other lienholder and shall procure the receipt of the county treasurer therefor, showing the mortgage or other lien relationship of the person paying such taxes, and the same shall have been recorded with the county auditor of the county wherein the said real estate is situated, within ten days after the payment of such taxes and the issuance of such receipt. It shall be the duty of any treasurer issuing such receipt to make notation thereon of the lien relationship claim of the person paying such taxes. It shall be the duty of the county auditor in such cases to index and record such receipts in the same manner as provided for the recording of liens on real estate, upon the payment to the county auditor of the appropriate recording fees by the person presenting the same for recording: AND PROVIDED FURTHER, That in the event the above provision be not complied with, the lien created by any such payment shall be subordinate to the liens of all mortgages or encumbrances upon such real property, which are senior to the mortgage or other lien of the person so making such payment.
RCW 84.56.330
Effective date-1999 c 233: See note following RCW 4.28.320.