RCW 84.56.060: Tax receipts—Current tax only may be paid.

The county treasurer upon receiving any tax paid in cash, shall give to the person paying the same a receipt. The treasurer shall record the payment of all taxes in the treasurer's records by parcel. The owner or owners of property against which there are delinquent taxes, shall have the right to pay the current tax without paying any delinquent taxes there may be against the property.