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I'm not sure I understand what you mean by "estimated payments". On your federal return estimated payments are payments toward your final federal tax or state individual income tax which you don't have in Washington state.
Are you talking about where to report them on your personal return? Is that where you are reporting your business activity, on a Schedule C? If so, that's where the Washington state business tax would be reported on your federal return.
If that isn't what you mean, please clarify further exactly what you are asking.
Schedule C, line 23
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Thanks very much, Steve G.