We have a strong septic odor in our house that seems concentrated in the crawlspace below. The odd thing is that the odor only becomes noticeable in a strong rain (even flooding due to snowmelt doesn’t cause the same condition). I’ve made sure all the traps are sealed. The only thought I have is that the water coming down the vent pipe is blocking the vent and causing gas to be vented through an otherwise unnoticeable leak or even through the traps. Any suggestions?
If you have horizontal lines inyour attic they could have the wrong pitch or a sag in the line and when it rains it could fill up blocking your vent and then when you flush it could pull water out of your traps creating the smell Good luck