The general rule is: your report all your income on your home state return, even the income earned out of state. You file a non-resident state return for the state you earned income in and pay tax to that state. Your home state will give you a credit, or partial credit, for what you paid the non-resident state. You will have to file a non resident GA state return and pay GA tax on the income earned there.
Since WA does not have an income tax, you get no credit but do not have a resident return to file. But you still have to pay tax on that income to GA.
