I have this house built back in 1957 or so and getting this bad odor coming from our basement. Can not tell if it a dead animal, a sewage gas smell, or something burning. I first thought that it was the sewage smell. The sewage trap drain locate in the middle of the floor, so I started flushing that drain with water over and over again. This is what I was told to do by Water Works when this happen about two years ago. The drain is holding it water in the trap without a problem as far as I can tell. Anyway this did not help. The smell will come and go. Sometime worst than others, but always the strongest in the basement by the sewage drain/ Furnance/ and the entry door of the house. Of course the furnace keep circulating the problem throughout the house. Hard to narrow down the exact location. Call out Water Works again and they said that their meter did not pickup any gases. That was good to here but did not resolved my problem. They thought it maybe a dead animal in my duct work because it seem then that the furnace set the odor off. Call in an HVAC Tech, they did not find anything within the duct work and vents and the smell was not as pronounce when they arrived. I took the Furnace apart for inspection and cut out my drywall ceilings and took apart most of the duct work and inspected it where the smell lead me and found nothing. This has been going on for 5 days now. Last night I did notice that when the washer machine was running water that the smell got worst, but I also thought that was the case when the furnace turn-on as well before last night about 3 days ago. I have even purchase a see-snakes from ridgid the help with the search with no luck. Water Works mention that my main sewage drain pipe runs strange out to the front of the house to the streets and the sewage trap drain pipe run in an angle from the center of the basement floor over to the main sewage drain to joint up together. Can someone help me with ideas on how to narrow down this problem? I am almost positive that it is a problem with my main sewage drain at this time now. If you feel the same way, what do I need to do to get rid of this smell. It is killing me and my Family. I have a City sewage system for this house.

Thank you very much

By "sewer drain" are you referring to a floor drain? What I thinks happening is that you may have a partial blockage in the main. When a flush hits the clog it bounces back sending a bubble of sewer gas ahead of it. It's just possible that the back pressure pushes a bubble of sewer gas past the trap in the floor drain and out where the cold air return in your furnace picks it up and sends it through your house. That's about all I can come up with. Regards, try snaking everything downstream from the floor drain. Good luck, Tom