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From the sound of it you understand the issue pretty well.... however if the pit and its vent are tight, isolating it from the rest of the plumbing may very well not solve the problem.. the odor could be coming from bad venting elsewhere in the system
You and I will have to mull this over for a while.
Can you tell me if the pit accumulates any water from the rest of the system when the toilet is not in use? can we plug the pipe connected to the pit that allowed smoke to the main vent stack as a test? If so, tell me what size that pipe is what it is made of please
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The pit only accumulates water from the bathroom fixtures (toilet, sink, shower). I have never heard the pump kick on or water draining to the pit unless one of these is being used.
Getting access to any of these pipes is difficult/costly as the basement is fully finished. I had on opportunity to feel around behind the walls a few months ago when we replaced the utility sink and was able to get shoulder deep and feel around pretty good. That is when I confirmed for myself tha the utility room was draining to the main stack but venting to the pit vent. But would probably do the test you have in mind before I get to point of ripping out major drywall. The damage would be more isolated in doing the test.
All venting pipe discussed is 2.5 inches in diameter, PVC pipe.
One other thing I forgot to mention is that after I got the lid fixed I was somewhat convnced that the odor must be some funky mold problem behind the walls. I even did cut into some drywall in various areas and it is bone dry beind these walls. Since then, on three occassions we have gone out of town for two weeks or more and the smell is 100% completely gone when we get back. It comes back over the first few days back and is pretty much constant after that. That is what convinces me we are dealing with a sewer gas problem and not some funky mold problem. If it were mold it wouldnt go away like that. Definately associated with living in and using the house. Those two week periods have been in the summer, fall and winter. So it doesnt seem to be associated with the gas boiler (which we also had checked for leaks and we are OK there). Only thing left in my mind is a sewer gas issue. Plus it smells to me just like the smell we had when the lid was leaking, only much less now.
While we think about solutions or tests, i wonder if you think there is anything technically wrong with the setup I described. In other words If all aspects were airtight on it, would it still be a potential problem? I can find guys on the internet saying stuff like "your ejector pit MUST have a dedicated vent that doesnt connect with anything else." But you know how that goes...I can find guys on the internet saying they own a square triangle too.
Hello again, its a sticky issue since we cannot see the piping, its condition or any design errors.
How hard would it be to put a deep trap in the pit pump discharge line, and possibly fit a sewage rated check valve in between the pump and the trap,
Since smoke is getting past the pit and to the main vent stack, we can be fairly sure that the check valve is not closing completely tight. Thats one way to look at it.
If the pit discharge line is connected to the top of the of the main waste line, or the vent stack, sewage would not flow back to the pit through the leaking check valve, but sewer gases would.
Lets think about that for a bit.... replacing the check valve has maybe a 90% chance of solving the problem. A trap on second thought would not solve the problem and could solidify in time,
Hello again, thanks for the clarification on the smoke route from the pit to the main vent stack.
Its a bit complex... i think I might have a better idea now however. Tell me if this seems accurate.
Your sinks are currently connected to both the main stack vent and the pit vent line by means of a tee in the vent line.
If that is correct you should be able to cut and cap the vent line from the sinks to the main stack as you have suggested...and the sinks should vent adequately via the vent line from the pit. ...IF... the line slopes continuously down from the sinks to the tee on the pit vent line.
You can try cutting the line from the sinks that runs to the main vent stack and fitting two pipe caps but without glue... then fill and drain the sinks. If everything works that way... then glue the caps on.
If that fails you can fit a compression type repair coupling in the line you cut to restore that function if you have to.
Let me know, we can go from there