Wash. Rev. Code § 6.27.220
If the answer of the garnishee is controverted, as provided in RCW 6.27.210, the garnishee may respond by affidavit of the garnishee, the garnishee's attorney or agent, within twenty days of the filing of the controverting affidavit, with copies served on or mailed by first-class mail to the plaintiff at the address shown on the writ and to the defendant as provided in RCW 6.27.210. Upon the expiration of the time for garnishee's response, the matter may be noted by any party for hearing before a commissioner or presiding judge for a determination whether an issue is presented that requires a trial. If a trial is required, it shall be noted as in other cases, but no pleadings shall be necessary on such issue other than the affidavit of the plaintiff, the answer of the garnishee and the reply of the plaintiff or defendant controverting such answer, unless otherwise ordered by the court.
RCW 6.27.220