Wash. Rev. Code § 5.44.140
In any proceeding regarding the determination of a family relationship, including but not limited to the parent and child relationship and the marriage relationship, a determination of family relationships regarding any person or persons who immigrated to the United States from a foreign country which was made or accepted by the United States citizenship and immigration services at the time of that person or persons' entry into the United States creates a rebuttable presumption that the determination is valid and that the family relationship under foreign law is as made or accepted at the time of entry. Except as provided in RCW 26.26A.115(2), the presumption may be overcome by a preponderance of evidence showing that a living person other than the person named by the United States citizenship and immigration services is in the relationship in question.
RCW 5.44.140