Wash. Rev. Code § 51.12.160
The services of employees of a foreign degree-granting institution who are nonimmigrant aliens under the immigration laws of the United States, shall, for the purposes of RCW 51.12.120, be considered to be localized or principally localized, in the country of domicile of the foreign degree-granting institution as defined in RCW 28B.90.010 in those instances where the income of those employees would be exempt from taxation by virtue of the terms and provisions of any treaty between the United States and the country of domicile of the foreign degree-granting institution. However, a foreign degree-granting institution is not precluded from otherwise establishing that a nonimmigrant employee's services are, for the purpose of such statutes, principally located in its country of domicile.
RCW 51.12.160