I am getting a sewer gas smell kind of a bad flatulence smell that is intermittent and I can feel a little draft coming up over the shower drain. I never have had this happen in this home before and have lived in it almost a year. It is about 0 to -20 degrees right now and I wonder if it is weather related. I removed the tank lid to the septic and all looked good and was full of only water no sludge build up. I did have to break the snow and ice out of the drainfield line vent and I thought that would cure it. There is no obstruction in the drains i.e... Hair soap etc.. I am wondering if the weather could affect the venting and cause pressure to back up. My septic was new 2 years ago 1 year before I puchased home. 1 old line to old septic was being used to drain the kitchen sinks but it started to drain slow and backed up into basement floor drain every time I drained the kitchen sinks so I rerouted the kitchen sinks to the new septic system, both sinks have a p trap and one before entering the 3inch black line and there is no smell around it or the sinks. I plugged the old vent to the roof and down to the septic and expandable foamed the floor drain. Anything obvious jump out at you experts.

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I can feel a little draft coming up over the shower drain.

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Is there a "draft" from both shower drains or just one?
That "draft" is the cause of the sewer gas you smell. This should not happen if the trap seal's intact. Take a stick and push it down the drain to the bottom of the trap. It should come back with about 2 inches of water on it. If not then let me know. Do you hear any gurgles or bubbling coming out of the traps in question? It could be your vents are iced up and the suction of draining water's pulling the trap seals down, but you would hear some sort of sound from the shower traps if that were the case. Check the trap seals and let me know what you find. Back to you. Tom

Hey speedball thanks I knew that there shouldn't be any updraft so I had checked the vent for the septic and found one iced up but after a call to the former owner found another had been installed and it was connecting old tank to new septic tank. So after digging in the snow on a search mission for it I found it and cleared it and it immiediatly remedied the problem, Why it was left at ground level in the grass I will never know but I added an elbow and uppipe and a vented weather cap and it has gone away. Thanks. P.S. I probably had some gurgleing in that lower shower but almost never use it so I would not have heard it. I even ran the shower thinking maybe the p trap had dried up in the -20 weather and was not functioning.