Wash. Rev. Code § 85.15.090
The decision of the board of county commissioners upon any objection made within the time and in the manner prescribed may be reviewed by the superior court of the county wherein the property in question is located, upon appeal thereto taken in the following manner: Any person aggrieved must file his or her petition for writ of review with the clerk of the superior court wherein the property is located within ten days after the roll affecting such aggrieved party was adopted by resolution, and serve a copy thereof upon the county treasurer. The petition shall describe the property in question, shall set forth the written objections which were made to the decision, and the date of filing of such objections, and shall be signed by such party or someone in his or her behalf. The court shall forthwith grant such petition if correct as to form and filed in accordance with this chapter.
RCW 85.15.090