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Sewer gas problem

For the past year or so, we have had episodes of sewer gas backing up through our main floor bathroom sink. It comes in quickly and wicked! It usually happens when the wind is blowing, so I thought the wind was probably causing a downdraft that was sucking the water out of the trap. However, the water is never sucked out of the toilet bowl which is directly next to the sink. This week however, it happened twice when no wind was blowing. My husband climbed up and ran rods down the pipe to see if it was blocked. It was not. We have another bathroom directly below the one where we are having the problem, but we never smell the gas down in the basement. I must also add that this is a 1947 house built by amatures, and there is only the one vent in the house. The kitchen on the opposite side of the house has no vent other than an open extension on the pipe that drains the sink and dishwasher into the sewer line. (which plugs up periodically--but that is another story). Does anyone have any idea as to what may be causing this. I would sure hate to have the gas fill the house when we are gone, or at night when we are asleep.
PS--we live in Montana with lots of weather and temperature changes

Re: Sewer gas problem

Generally when you get sewer gas coming into the house it is due to a dry trap or a blocked or improperly installed vent. A possible cause is no vent to the sink line and when the toilet is flushed it sucks the water out of the trap. You might be able to install a Studor vent after the sink trap. http://www.studor.com/mini-vent.htm


Re: Sewer gas problem

Recently my dishwasher has been releasing an awful smell from my garbage disposal. I assume it is sewer gas however, I do not know why it just started or what to do. I have run the dishwasher and the garbage disposal clean . Still no help..Any suggestions?

Re: Sewer gas problem

Is the trap on the sink made of white plastic?

If so, you can shine a strong light from behind it and actually see the water level in it.

Do this while somebody flushes the toilet to see if the flushing affects the water level in the sink trap.

It may happen that you see the water level in the sink trap fluctuate, or even get sucked out.

If you can't see the water level this way, next best is to look straight down into the sink drain to watch the surface of the water level. Remove the stopper to see better.

If you see, by either method, that the water level is affected by the flushing of the toilet, you can add an air admittance valve (Studor is one brand, Oatey is another), which is simply a one-way air valve that allows air to enter the pipe, but does not allow sewer gas to escape. It's not as good as a properly installed vent, but it would solve the problem described above.

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