On 2008-06-12, franz fripplfrappl wrote:

Already checked: vent cannot be smaller than 1/2 of pipe. A 2" works
just fine with the 3" system.

There is also typically a requirement that the aggregate vent size be
at least as large as the building sewer (main drain). Or sometimes
there is the stronger requirement that at least one vent is as large
as the building sewer. Just FYI.

Cheers, Wayne