Wash. Rev. Code § 7.28.130
The defendant shall not be allowed to give in evidence any estate in himself, herself, or another in the property, or any license or right to the possession thereof unless the same be pleaded in his or her answer. If so pleaded, the nature and duration of such estate, or license or right to the possession, shall be set forth with the certainty and particularity required in a complaint. If the defendant does not defend for the whole of the property, he or she shall specify for what particular part he or she does defend. In an action against a tenant, the judgment shall be conclusive against a landlord who has been made defendant in place of the tenant, to the same extent as if the action had been originally commenced against him or her.
RCW 7.28.130