Wash. Rev. Code § 88.32.090
Any person who feels aggrieved by the final assessment made against any lot, block, or parcel of land owned by him or her may appeal therefrom to the superior court of such county. Such appeal shall be taken within the time, and substantially in the manner prescribed by the laws of this state for appeals from justice's courts. All notices of appeal shall be filed with the board of county commissioners, and served upon the prosecuting attorney of the county. The clerk of the board of county commissioners shall at appellant's expense certify to the superior court so much of the record, as appellant may request, and the cause shall be tried in the superior court de novo.
Any person aggrieved by any final order or judgment, made by the superior court concerning any assessment authorized by RCW 88.32.010 through 88.32.220, may seek appellate review of the order or judgment in accordance with the laws of this state relative to such review, except that review shall be sought within thirty days after the entry of such judgment.
RCW 88.32.090
Severability-1988 c 202: See note following RCW 2.24.050.