"Jim Macklin" wrote

I think a lot of people are going to Home Depot or Lowes and
doing their own plumbing and not following CODE. A
qualified plumber can tell pretty quickly what the problem
is, but a fix can involve considerable re-work if new vent
pipes must be run.

Fortunately, a popup kind of vent is now available and legal (in most cases)
and the venting can be had with a minimum or "surgery."

You are right about the non-code bit, and also would be surprised at what
does pass, even when it is inspected.
--
Jim in NC