Wash. Rev. Code § 7.05.310

(1) The parties are free to agree on the place of arbitration. Failing such agreement, the place of arbitration shall be determined by the arbitral tribunal having regard to the circumstances of the case, including the convenience of the parties.

(2) Notwithstanding the provisions of subsection (1) of this section, the arbitral tribunal may, unless otherwise agreed by the parties, meet at any place it considers appropriate for consultation among its members, for hearing witnesses, experts, or the parties, or for inspection of goods, other property, or documents.