Washington Revised Code Title 82. Excise Taxes § 82.87.120. Joint filers--Separate filers--Tax liability

(1) If the federal income tax liabilities of both spouses are determined on a joint federal return for the taxable year, they must file a joint return under this chapter.

(2) Except as otherwise provided in this subsection, if the federal income tax liability of either spouse is determined on a separate federal return for the taxable year, they must file separate returns under this chapter. State registered domestic partners may file a joint return under this chapter even if they filed separate federal returns for the taxable year.

(3) The liability for tax due under this chapter of each spouse or state registered domestic partner is joint and several, unless: