Wash. Rev. Code § 85.06.670
In carrying out the foregoing powers, or any other powers possessed by the board of commissioners of such district, said board shall have authority to acquire by lease, contract, private purchase, or purchase at any sale, any real or personal property and to sell any real or personal property, or any part thereof, owned by said district when they find that the usefulness thereof to such district has ceased. Such board shall also have authority to enter into contracts with any other diking and/or drainage district, person, public or municipal corporation, flood control district, state, or the United States, with reference to sharing the costs or expenses of improvements for said district or the protection thereof, and bind its district by such contract.
RCW 85.06.670