Okay. I've been trying to figure this out for a while. When the heat and A/C comes on I will get a rotten egg smell in the house from time to time. I've cleaned the coils and run bleach down the condensation drain. So I was looking around tonight and it seems like the smell is coming from around the washer drain and is being sucked into the heating fan and circulated through the house. I pulled the cover that covers the washer drain tube. The pipe runs down into the p-trap and then runs through a t-pipe that goes down to the septic tank and up to a vent. I'm not a plumbing expert, but this doesn't seem right I know the p-traps are there to keep gases from coming back into the house so why would there be a vent after the p-trap that can allow those gases directly back into the house. I need help and I need it quick. I'm trying to sell my house and trying to show a house that smells like rotten eggs just isn't going to work.