We had the plumber out to check the gas smell in the bathroom. He put a new wax ring on the toilet. It seemed to do the trick but the smell is back. I understand that we may have a clogged vent pipe but my husband wants to save plumber costs. Is there a liquid we can pour down the vent pipe or is using an auger or hose stream the only effective method. Thanks.

Where does the smell come from? If it is under the toilet, have the plumber come back and install a thicker ring. Is the toilet tight to the floor? Smells from a vent are common and expected. A plugged vent would also cause gurgling in the toilet and/or sinks as the gasses vent through them. If all of the fixtures drain properly, I don't think you have a plugged vent.

I agree with Brian,
If your fixture traps don't gurgle and talk to you when you flush or drain chances are the vent's clear.
Your nose is the best detective here. Sniff around the base of the bowl band the other drains, Where's the smell the strongest? Let me know, Tom

Did your plumber caulk around the base of the toilet ?

Milo