Wash. Rev. Code § 79.125.240
All state-owned tidelands and shorelands, otherwise permitted under RCW 79.125.200 to be sold, shall be sold on the following terms: One-tenth to be paid on the date of sale; one-tenth to be paid one year from the date of the issuance of the contract of sale; and one-tenth annually thereafter until the full purchase price has been made; but any purchaser may make full payment at any time. All deferred payments shall draw interest at the rate as may be fixed by rule adopted by the board, and the rate of interest, as so fixed at the date of each sale, shall be stated in all advertising for and notice of the sale and in the contract of sale. The first installment of interest shall become due and payable one year after the date of the contract of sale and all interest shall become due and payable annually on that date, and all remittances for payment of either principal or interest shall be forwarded to the department.
RCW 79.125.240