Wash. Rev. Code § 87.19.050
Bonds issued under and by virtue of this chapter may be exchanged for outstanding bonds at not less than the par value of the bonds refunded or may be sold at not less than ninety percent of their par value, and all money derived from the sale of such bonds shall be applied to the redemption of any or all of the outstanding bonds of said district to be refunded and any such outstanding bonds so refunded shall be endorsed in red ink "Refunded Bonds" and filed and preserved for one year and then destroyed by the county treasurer in the presence of witnesses: and the secretary of said district and the county treasurer of said county shall keep a record of such bonds so refunded and shall note the date of the refunding and the date of the destruction of the refunded bonds and in whose presence they were destroyed.
RCW 87.19.050