Wash. Rev. Code § 34.05.455

(1) [(a)] A presiding officer may not communicate, directly or indirectly, regarding any issue in the proceeding other than communications necessary to procedural aspects of maintaining an orderly process, with any person employed by the agency without notice and opportunity for all parties to participate, except as provided in this subsection:

(a) [(i)] Where the ultimate legal authority of an agency is vested in a multimember body, and where that body presides at an adjudication, members of the body may communicate with one another regarding the proceeding;

(b) [(ii)] Any presiding officer may receive aid from legal counsel, or from staff assistants who are subject to the presiding officer's supervision; and

(c) [(iii)] Presiding officers may communicate with other employees or consultants of the agency who have not participated in the proceeding in any manner, and who are not engaged in any investigative or prosecutorial functions in the same or a factually related case.

(d) [(b)] This subsection does not apply to communications required for the disposition of ex parte matters specifically authorized by statute.

(2) Unless required for the disposition of ex parte matters specifically authorized by statute or unless necessary to procedural aspects of maintaining an orderly process, a presiding officer may not communicate, directly or indirectly, regarding any issue in the proceeding, with any person not employed by the agency who has a direct or indirect interest in the outcome of the proceeding, without notice and opportunity for all parties to participate.

(3) Unless necessary to procedural aspects of maintaining an orderly process, persons to whom a presiding officer may not communicate under subsections (1) and (2) of this section may not communicate with presiding officers without notice and opportunity for all parties to participate.

(4) If, before serving as presiding officer in an adjudicative proceeding, a person receives an ex parte communication of a type that could not properly be received while serving, the person, promptly after starting to serve, shall disclose the communication in the manner prescribed in subsection (5) of this section.

(5) A presiding officer who receives an ex parte communication in violation of this section shall place on the record of the pending matter all written communications received, all written responses to the communications, and a memorandum stating the substance of all oral communications received, all responses made, and the identity of each person from whom the presiding officer received an ex parte communication. The presiding officer shall advise all parties that these matters have been placed on the record. Upon request made within ten days after notice of the ex parte communication, any party desiring to rebut the communication shall be allowed to place a written rebuttal statement on the record. Portions of the record pertaining to ex parte communications or rebuttal statements do not constitute evidence of any fact at issue in the matter unless a party moves the admission of any portion of the record for purposes of establishing a fact at issue and that portion is admitted pursuant to RCW 34.05.452.

(6) If necessary to eliminate the effect of an ex parte communication received in violation of this section, a presiding officer who receives the communication may be disqualified, and the portions of the record pertaining to the communication may be sealed by protective order.

(7) The agency shall, and any party may, report any violation of this section to appropriate authorities for any disciplinary proceedings provided by law. In addition, each agency by rule may provide for appropriate sanctions, including default, for any violations of this section.