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