Most of the codes allow the automatic vents, but for whatever reason, a lot of towns do not. This is the case with my town. The inspector said that my town uses the 2006 NSPC (National Standard Plumbing Code), and does not make any town specific amendments to it. Section E.8 of the NSPC is what allows "Air Admittance Valves", yet for whatever reason, my town inspector said he won't allow it. Go figure.