I'm having a problem lately with sewer gas venting into the bathroom from either the base of the toilet or the tub drain. It comes from the shower/tub drain only during use when the wind is from the South (vent is on the N slope of the roof). Also, from the toilet base when the wind is from the South. My guess is that the wind is pushing the gas back down the vent & into the system so I'm considering putting some sort of guard over the roof vent; maybe a 90° or 45° PVC elbow. I also notice a hint of the gas coming out of the bathroom heater vent when the furnace is on - no matter what the wind direction.
This is a new problem this year after tiling over a hardwood bathroom floor this spring & insulating the attic last winter so I'm trying to make a connection with how these things might have contributed to this new problem. The toilet & tub sit higher now due to the tile & backer board but the toilet isn't leaking water so I don't think that's the issue. It is a claw foot toilet so the p trap is below the floor. I am on a septic system but don't have any issue with the drains not draining so I don't think it needs pumped. I just can't figure why it's only a problem when there is a South wind but can only think of the above mentioned fix of using the PVC elbow??
Any other ideas would be appreciated.