A friend has a sewer treatment plant for a rural home. She's on city water, but not for sewerage. Only in her bathroom, not any of the other 2 toilets in the house, is there a sewer smell in the flushed toilet water. The treatment plant is one that is motorized and suppose to treat sewerage before discharging it into a ditch along the road. She is also hearing an air noise in the wall, guessing in the vent pipe that vents through the roof. We're trying to figure out what's causing the smell and then only in her toilet, when the bathroom next door on the same side of the house has no smell. She also checked around the base of the toilet and the wax seal appears to be OK, no water leaking. When she flushes, the water in the bowl, although clean looking, has a sewer smell. Can you advise how she should proceed? Thanks! Lp 6/15/11

"She also checked around the base of the toilet and the wax seal appears to be ok, no water leaking" This is faulty thinking, a wax ring can be totally shot and still not leak water. All it has to do is leak sewer gas. I'd check this further by sealing the base of the toilet to the floor with modeling clay for a temporary seal. If the smell goes away you found the issue

If you somehow had a cross connection to that toilet I could possible see it smelling that way. However, I think HB has the right answer, many smells will emanate through the wax ring and no water leaks.

Thanks for the tip. She will try clay around the base as a first resort. Hopefully this works, because it's the easiest to fix. Thanks again!

The clay is just a temporary fix, if it works do not just leave it in place. The wax ring is fairly easy to replace and cheap, about $3.00

You were right. The clay stopped the smell. Thanks a lot!! Saved her much unnecessary expense. Take care! Lp

The air sound is still occurring in the wall behind the toilet, which she assumes is where the vent pipe should be located. Can you advise what could be causing the air noise? Thanks again for your assistance. Lp 6/20/11

That sound could be air trying to vent via the vent stack which continues up and out the roof, like youmentioned in post #1. . If its is resyticted there can be a swoshing noise. To rod out a vent you need to be on the roof and use enough snake to reach roof top to basement floor plus 20', only do this if it is safe to be on the roof and you are steady. Otherwise call 3 plumbers for bids.

Hey ballengerb1. Nice call with the molding clay. Never heard of that before. Great idea for homeowner trouble-shooting. Thanks for the tip.