Wash. Admin. Code § 381-50-150
All relevant evidence shall be admissible which, in the opinion of the presiding officer, is the best evidence obtainable, having due regard for its necessity, availability, and trustworthiness. "Relevant evidence" means evidence having a tendency to make the existence of any fact that is of more consequence to the determination of the action more or less probable than it would be without evidence. In passing upon admissibility of evidence, the presiding officer conducting the hearing shall give consideration to, but shall not be bound to follow, the rules of evidence governing civil proceedings in matters not involving trial by jury in the superior courts of the state of Washington.
The presiding officer may, either with or without objection, exclude inadmissible evidence, or order accumulative evidence discontinued. Parties objecting to the introduction of evidence shall state the precise grounds of such objection at the time evidence is offered. If the sole evidence is hearsay that would be inadmissible in a superior court proceeding and is not substantiated or corroborated, or is the result solely of a polygraph examination, a finding of guilty shall not be made.
Wash. Admin. Code § 381-50-150
92-22-008, § 381-50-150, filed 10/21/92, effective 10/19/92. 91-14-029, § 381-50-150, filed 6/26/91, effective 7/27/91.