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Hi, hoping someone can assist with this issue and possibly shed some light. We bought a chalet in May. Everything was fine until late December when we began noticing a bad, bad sewer smell. I had the main line scoped, plumber said that it was intact all the way to the septic tank, however he found a Y off the line headed somewhere under our finished wide plank floor in our walkout basement. He thought perhaps we had an open drain venting gas into our chalet. After removing several boards, I found the drain. It was plugged with dried sludge from a previous backup sometime in the chalet's history. I cleared the drain, it now holds water in the trap beautifully. We thought that might be the problem solved, but no such luck. Here is what happens:

We arrive at the chalet, there is really no smell. We begin using the plumbing, the smell starts to accumulate. It is the worst in the basement walkout living room. The place where the smell emanates from is the concrete slab relatively on top of the main line about two feet from where the line exits the house and runs to the septic tank. This location is also roughly in the same area as the aforementioned drain. It also, by the looks of the concrete, is where some effluent puddled and settled/soaked into the concrete when the backup occured. The drain, however, does not stink now that it is cleaned. The concrete does. If I put my nose to the concrete prior to system use, I'd put the residual smell of the area at about a 3 out of ten. After running the shower for 10 minutes, I would put it at a 18 out of 10 (yes, it's on a Spinal Tap scale). It's like a sewer is wafting out of the concrete. Thoughts? Here is what we have done so far regarding vents, etc:

- scoped main line all the way to septic tank through cleanout, plumber says no break apparent
- snaked both roof vents with 25' snake, everything seems clear as I can see gas venting from both stacks
- poured gallons of warm water down both vent stacks, just in case to flush anything possibly in them
- camera scoped between sleepers under wide plank flooring in basement and have ascertained through visual that single floor drain is likely only floor drain extant in basement, likely eliminating possibility of a dry trap
- smell test with nose between sleepers as water running to detect for smell/air movement. None present.
- cut into drywall low along two walls to see if I could find a vent for floor drain coming up through slab. None seems to exist, eliminating possibility of a cut vent line in basement room
- smell test conducted on concrete slab with smell at aforementioned location being extremely intense with shower running
- exterior of house at ground level and above directly on other side of interior wall everything smells normal, no sewer smell. Septic tank location is about 8' past this exterior wall.

I think that is about it. This is driving me crazy. Help!!!


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good luck it some times takes a lot of steps to find and a lot of time. start by blocking floor drain if your furnace has a condensate line taped into drain system test that then isolate and back track each pipe until you find it. you might see about using a strong fragrance and put it down each drain or a gas sniffer and see when and where it starts. not fun and it can get frustrating we ran over 1500 feet of pipe between second floor and first floor finished drop ceiling past first air pressure test but on finale it would not hold took 4 guys 3 days to find
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