We noticed a sewer smell in the add-on bathroom a few months back. Aerobic service guy came out and determined our air pump was out and replaced it. Smell continued, so we had the tank pumped. Smell continued, discovered a broken air line to the aerator which was replaced. Smell continued. I noticed the toilet had shifted and pulled it and replaced the wax ring with the newer fluid master rubber gasket. Smell continues. Snaked all drains in the bathroom and the vent tube, smell continues. That being said, the smell went from you could walk into the garage we took in and the smell hit you to the smell only bothers you after sitting all day/night in the bathroom and after the toilet is flushed, no smell. Also, smell comes up from toilet when the water is disturbed. No smell is coming from any other drain (sink, shower, or tub). Sometimes there is no smell at all, and then it comes back. I have noticed the same about the aerobic system, sometimes there is still a smell, sometimes not. The service guy says his people have come out and aerobic system is fine and there must be a vent problem. Toilet flushed fine, no gurgling, and all drains work fine. Anyone have an idea? Is it possible the fluid master gasket isn't working like the wax does? Any input is appreciated.

Have a licensed - bonded - insured plumber set the toilet PROPERLY.

Flange sitting ON TOP OF the finished floor AS PER CODE.

Flange bolted THROUGH said floor to a structural member.

The wax ring (theoretically) acts merely to seal off the sewer gas.

The liquid 'squirts' from the 'nozzle' into the 'funnel' where it flows away by gravity.

The outlet of the toilet horn should be LOWER than the top of the flange.

The 'ideal' clearance would be 1/8 - 3/16".

Toilets are 'hollow' on the bottom so that the flange fits INSIDE the base.




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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

There is no magic other than the good old process of elimination.

I would say if you suspect the smell is from one of the bathroom fixture drains, my suggestion would be to open the window and air out that bathroom to get rid of the smell, then use duct tape to tape the sink drain hole, the shower or tub drain hole, the tub overflow and along the entire bottom of the toilet bowl where it meets the floor. Do not use that bathroom for a day, and see if you still detect that smell. If it disappears, then it's one of those your taped up. Remove them one at a time a day apart and see which one is the culprit.

Sometimes it may not be the drains, any chance you have an AAV somewhere inside a cabinet or behind walls that may have failed?

Is this bathroom air conditioned? Is there an HVAC vent? Years ago I experienced a sewer odor in an office and after a long period of investigation, it was caused by an AC handler unit hung in an attic with a condensate drain connected to the sewer line (bad idea) without a trap (bad idea). When the AC turns on the air handler sucks all the gas in the line upward from the drain pan and blows it all out into the office.

There is no AAV, and yes there is a HVAC vent. Problem is the smell seems to be from the water in the toilet bowl, flush and it goes away. Disturb the surface (urinate), the smell becomes worse. Flush and it seems to go away. So I changed the rubber seal back to a wax seal. The smell is still there and worse now at times and is like it is coming up through the water in the toilet and not from around the base. I am definitely scratching my head on this one. As for windows, none. There was no overflow and no odor coming from the other drains. Just standing over the toilet. And it all started when the septic tank had problems. Probably coincidental, I know, but dang, nothing else seems to fix it.



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Do you have a proper sized vent pentrating the roof? Make sure birds have not pooped and caused a partial blockage on the end of pipe at that vent.

Process of elimination:

First check the vent for partial or full blockage.

Then, since you have no problem removing the toilet to replace wax rings, remove it again, and wrap it tightly in a large plastic garbage bag so no odor can emerge. You may need one bag for the tank and one for the bowl. If possible, remove the bagged toilet to a garage or outdoors. Seal the waste hole tightly as well, tape plastic tightly over the entire flange.

If the smell stays in the bathroom, the source is in the waste or vent system, likely cracked pipes somewhere below the flange or in the walls. If the small is eliminated, unwrap the toilet after a couple of days and see if it smells. Continue the process of elimination.

In my case, when I started disassembling the bathroom, I found the sink waste line behind the trap had never been installed properly when the house was built. Easy fix.

So as strange as it suddenly came, the mystery odor has gone. I did nothing else since putting the new wax ring on the bottom, and it just suddenly decided to play Bigfoot and disappear. Like the center of a Tootsie roll pop, I guess we will never know what caused it.

And now I may know why....Septic service guy just messaged me he came out last week, disconnected and reconnected the fittings, and now miraculously everything is fine. I guess a bad connection out there causing problems inside.

So, I appreciate the help everyone provided, but I discovered the cause/cure for my problem. The smell returned. I was checking under the cover of my pump to make sure ants weren't trying to bed up under there like they have in the past and heard a wisp of air coming from under. I moved my hand around and discovered air gushing out of the fittings from the pump to the system. I pushed the pipes together, no more air leak and no more smell. Septic guy didn't glue the fittings.



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Thanks for the update. Am glad you found the cause.