The AAV doesn't have to be outside. The whole point is that it is
inside and you don't have to run a vent line outside. The normal
function of an AAV is not to let sewer gases out, but letting air in
to help the lines drain better.
The real issue is whether your local code allows an AAV to be the sole
means of venting, and that _is_ an issue of letting sewer gases out.
Kind of odd that the expectorator shot it down on freezing issues
instead of blowing up your house issues.
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