RCW 47.87.120

Notwithstanding anything in the laws of either state to the contrary, the commission shall not be required to pay any tax or assessment, or any in lieu of tax or assessment, by either state, or by any political subdivision, municipality, or district thereof including, but not limited to, any property tax, sales and use tax, or other tax or assessment upon real or personal property acquired or otherwise under the control of the commission, or upon any activity or expenditure of the commission, or upon the revenues of the commission, except to the extent that a municipal corporation would be subject to such a tax or assessment.