Your expertise and experience valued. I'm a layman with a big problem I can't solve! We are at the top of a sewer/vent stack on the 30th floor of a tower. We replaced 15 year old high flow toilets during a total reno of 2 baths. Into both baths, we put the same two-piece, 1.28 gpf single-flush floor-mounted Duravit Stark 3 comfort height toilet http://www.plumbingforums.com/photo/post-reno-sewer-gas-smell-pics-323.html In one bath, no problems. In the other bath we have an intermittent sewer gas smell. This work was done by certified plumbers, with City permits and inspected and passed inspection. We did not move any existing drains, simply reno'd around & put new fixtures on existing ones. In the problem bath there is a shower drain: no smell. there is a sink drain: no smell. there is no smell in the wall-hung vanity (which is on the same wall as the sewer vent and smelly toilet) which our contractor tells us is open to the wall interior behind a cosmetic board. The shower is now large and extends over top of a former bathtub drain that has been sealed. That drain never smelled before reno and is now capped, siliconed and the space around it filled with rubber firestop per code. It is now under a fully tiled shower base. Plumber returned, lifted toilet, showed us he'd used a wax ring with black funnel. He added a second wax ring (no funnel) and re-set toilet. Note: when the toilet was off the air from the drain was blowing VERY hard into the bathroom. The building's plumbing system maintenance rep who came on-site at one point said that's entirely possible and normal at the top of a stack like this. (any comment? is it?) Other times we've had the drain exposed the air pressure has seemed neutral. After plumber re-set toilet, now with 2 rings, intermittent smell continued. Although not every time, often smells after we finish showering. We turn on the bathroom fan before we shower & by the time we get out (10 minutes?) later it is smelling. It is also noticeable at times when we have our suite windows open and there is a wind. Building manager advised sewer gas smells have been experienced in other suites with negative in-suite pressure -- which ours has. They claim cutting the bottom off the suite door (to the hallway) has resolved it for others; we've done that and it has not resolved. We used painters tape to seal off the joins between toilet tank top & lid; between toilet tank bottom and toilet base; closed lid and sealed it to base. Did not resolve. Building plumbing system maintenance company advised vent was clear at the roof. We were also told that other suites would be reporting problems if the vent was plugged. We removed the toilet and with a plastic bag and tape, covered over the sewer drain and surrounding tile (attached pic). There was no smell during that time but it could have been that conditions just weren't right (assuming negative pressure is related). http://www.plumbingforums.com/photo/post-reno-sewer-gas-smell-pics-325.html Only guess from plumber, building maintenance manager, etc. was that negative pressure was too great for volume of water in the low-flow toilet; that sewer gas must be bubbling through the P-trap. They advised us to get a larger-flow toilet. However, we have never witnessed bubbling in the toilet bowl. there is no smell in the toilet bowl -- when we encounter the smell before it's spread far, it smells fresh in the bowl when the air around the toilet doesn't. I understand that the idea is more water in the bowl would provide more pressure against sewer gas bubbling through. However, I also understand now that more water in the tank doesn't necessarily mean more water in the bowl, and toilet specs don't seem to include water volume retained in the bowl (only water surface area which is not necessarily a measure of volume depending on bowl shapes). Instead of replacing the toilet with a larger flow one immediately, we replaced it with the same model to rule out a faulty toilet. This time we placed it ourselves. We removed the rings the plumber had placed: http://www.plumbingforums.com/photo/post-reno-sewer-gas-smell-pics-317.html http://www.plumbingforums.com/photo/post-reno-sewer-gas-smell-pics-316.html http://www.plumbingforums.com/photo/post-reno-sewer-gas-smell-pics-318.html http://www.plumbingforums.com/photo/post-reno-sewer-gas-smell-pics-319.html We were advised to use 2 wax rings, one with black funnel and another on top of that without. We did. http://www.plumbingforums.com/photo/post-reno-sewer-gas-smell-pics-320.html http://www.plumbingforums.com/photo/post-reno-sewer-gas-smell-pics-322.html http://www.plumbingforums.com/photo/post-reno-sewer-gas-smell-pics-321.html I wouldn't be surprised if we didn't get the toilet properly set on the wax ring as it is a very heavy toilet, has the modern skirt on it so there is no way to see the drain & toilet as you're placing it and the space is tight. I know the toilet was set down once in the vicinity of the drain before it was 'centered' and tightened. Smell continues. Recently walked in as it started to smell (weather had changed, wind was blowing & our suite windows were open). There was no smell in the toilet bowl but it was quite strong around the tank. I sealed the top of the tank with a plastic bag and tape, then set the lid on it. Smell recurred the next day. I removed the bag from the tank and there was no smell in the tank. But, it was very evident it was strongest behind the toilet, between the tank and the wall. The back of this toilet base is completely open (see attached pic) so the large open space will allow full opportunity for gas escaping the drain/seal to escape the base. Because space is so tight, we'd never be able to get a silicone seal around the back side of the base. http://www.plumbingforums.com/photo/post-reno-sewer-gas-smell-pics-324.html Other suggested causes: Sealed bathtub drain causing problems with venting. But, how could this be when there was no smell before and that drain wouldn't have served as a vent as it had a P-trap. Vent in wall is cracked or had a screw put in it during reno. But, assuming contractor is correct that back of vanity is open to the plumbing (not sealed with drywall), unlikely since there's no smell in the vanity. I'm leaning toward both wax ring installations being faulty. I don't know if it's that, if I need to start cutting into walls, or requesting our building maintenance people investigate anything else... Any input very welcomed. Thank you.