The Washington State Department of Revenue (DOR) has published a web page designed to educate tribes and tribal members/citizens about Washington State Taxes.

https://dor.wa.gov/get-form-or-publication/publications-subject/tax-topics/information-tribal-memberscitizens

What tribes and tribal members/citizens should know

• Tribal members/citizens do not pay state taxes for their transactions that occur in their Indian Country. This means state taxes are inapplicable when:
• You have a service performed for you within your Indian country.
• You purchase items within your Indian country.
• You pay for utilities, e.g., phone, water, electricity, trash collection, that serve your home or business in your Indian country.
• A product or service is purchased by you and delivered to you in your Indian country
• You own and operate a business in your Indian country; however, you may be required to collect state retail sales tax from non tribal citizen customers and report and remit the taxes collected.?

Tribal tax may, however, be due on any of the above. Ask your tribal government if tribal tax is due.