Washington Revised Code Title 8. Eminent Domain § 8.12.120. Interested party may be brought in

Such jury shall also ascertain the just compensation to be paid to any person claiming an interest in any lot, parcel of land, or property which may be taken or damaged by such improvement, whether or not such person's name or such lot, parcel of land, or other property is mentioned or described in such petition: PROVIDED, Such person shall first be admitted as a party defendant to said suit by such court and shall file a statement of his or her interest in and description of the lot, parcel of land, or other property in respect to which he or she claims compensation.