RCW 48.14.070

In event any person has paid to the commissioner any tax, license fee or other charge in error or in excess of that which he or she is lawfully obligated to pay, the commissioner shall upon written request made to him or her make a refund thereof. A person may only request a refund of taxes within six years from the date the taxes were paid. A person may only request a refund of fees or charges other than taxes within thirteen months of the date the fees or charges were paid. Refunds may be made either by crediting the amount toward payment of charges due or to become due from such person, or by making a cash refund. To facilitate such cash refunds the commissioner may establish a revolving fund out of funds appropriated by the legislature for his use.