Sewer gas from toilet

Hi! We have a new house and in every bathroom there is a smell of sewer gas, but only after someone sits on the toilet. Sounds funny, I know, but it's a very distinct odor. Any idea what would cause this? If it were a seal, would we smell it all the time? Thanks in advance!
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Jason Ducham wrote:

Just a thought...
See if the toilets rock a little when you push hard on them or have someone sit on them an shift their weight around.
If the installers did a lousy job of setting the toilets, they may rock enough to let the wax seals joining them to the waste pipes open a little and let some sewer gas out.
The water filled trap which keeps sewer gas from escaping through the toilet bowl is part of the toilet as you likely know, and if the seal between the toilet and the waste pipe sneaks open when the toilet rocks there's nothing to keep gas from escaping there.
Good luck,
Jeff
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Jeff Wisnia (W1BSV + Brass Rat '57 EE)

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<< Any idea what would cause this? >>
Adding to Jeff's suggestion, new house or not, there may be a venting problem. Look in this NG archives on this topic for creative ways to pinpoint athe problem. HTH
Joe
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Appears to me that if this is truly a new house, it is the builder's responsibility to fix it. If you mess around before trying to get them to correct the problem, they may claim that you caused the problem.
Walt Conner

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