Wash. Rev. Code § 32.08.148
In addition to all powers and authorities, express or implied, that a mutual savings bank has under the laws of this state, a mutual savings bank chartered under this title may exercise any powers and authorities at any branch outside Washington that are permissible for a savings bank operating in the jurisdiction where that branch is located, or for a bank, savings association, or similar financial institution operating in the jurisdiction if the laws of the jurisdiction do not provide for the operation of savings banks in the jurisdiction, except to the extent that the exercise of these powers and authorities is expressly prohibited or limited by the laws of this state or by any rule or order of the director applicable to the mutual savings bank. However, the director may waive any limitation in writing with respect to powers and authorities that the director determines do not threaten the safety or soundness of the mutual savings bank.
RCW 32.08.148