Starting today (July 1) there is no longer a retail sales tax exemption for sales to qualified nonresidents at the point of sale. See the Washington Department of Revenue’s page: https://dor.wa.gov/find-taxes-rates/retail-sales-tax/sales-nonresidents
Starting in January 2020, qualified nonresidents will be able to request a refund of the state portion of the sales tax for eligible purchases directly from the DOR. According to the DOR, qualified nonresidents are residents of six states, including Alaska, Oregon, Montana and Colorado, and American Samoa and some Canadian provinces. (Sales delivered to customers outside Washington are still exempt from business and occupation tax and retail sales tax as interstate and foreign sales.) More information is available at dor.wa.gov/nonresidents.