I have a basement toilet that is connected to a 4" buried sewer pipe but its vent that goes three stories up to the roof is only 2". The toilet seems to have a permanent smell of urine which starts even very soon after I clean it with Ajax and before anyone has used it. I understand the toilet has its own P or S trapping module intended to prevent backflow of gases from the pipe but could it be that the vent inadequately forces air out and some of it is finding its way indoors through the 1-2 sec period of flushing?

This is a hypothesis and I have no other explanation. My other toilets that are right next to a different, 4" vent stack don't smell and it has nothing to do with the cleaning or sanitation treatment. Moreover, I have a sewer access point (for snaking and cleanouts) above the toilet behind the wall and when I open the plug, it has the same smell as what collects inside the bowl.

  • Have you checked around the base of the toilet? The wax seal might be failing and the odor coming through the weep hole. check for any moisture.
    – JACK
    Feb 1, 2020 at 20:44
  • No, I put a brand new wax seal and then silicon around the perimeter of the base. Very tight, no leaks
    – amphibient
    Feb 1, 2020 at 20:45
  • Is it possible that the vent stack is leaking?
    – jwh20
    Feb 1, 2020 at 21:07
  • Or possibly clogged?
    – JACK
    Feb 1, 2020 at 21:09
  • or somebody is urinating on the floor
    – jsotola
    Feb 1, 2020 at 22:52

3 Answers 3


I would say NO, the vent is not the problem. A more likely culprit is a bad wax seal. I have found toilets with no water leakage and big gaps in the seal were someone tried to use silicone to seal the flange. No leakage and constant sewer smell. I pulled the toilet and was amazed. Cleaned probably a full tube of calking (calking gun size) out installed a .99$ was ring and the smell was gone.

Any residual smell may be from urine in the flooring and there are chemical treatments that can fix this.

Last if there is a floor drain it may be the cause of the smell, pour some water in the floor drain then add a cup of cooking oil this will keep the water in the trap from evaporating.
A clear vent even in a 3 story would not cause the smell you describe.


Check little used sinks, tubs, showers, laundry tubs, etc. Sometimes the “P-trap” will dry out (evaporate) and smell can come into the living space through the drain.

Pour a couple of cups of water down the drain to fill the “P-trap” and block any smells coming up through the drain.


At one point I had 4 boys and 2 girls in the house. For some reason the bathroom the boys used always smelled like pee. When the last one left and went to college, the odor stopped.

Someone may be missing the mark.

Vents generally do not smell like just pee, based upon my plumbing experience.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.