multiple choice - basement bathroom venting debacle and burps
I've been over this topic a bunch of times with "experts" and haven't gotten a single good answer....I hope you can help!
We are on septic. 12 year old house. It's gravity and in the backyard. Main house drain goes into the basement floor. 20 feet away, we have a basement bathroom. That drain also goes right into the cement floor.
I can't be sure, but I suspect that the bathroom drain meets up with the main house drain somewhere under the concrete or even near the septic tank.
Recently (and strangely, at this same time last year), every time someone uses water upstairs, the basement toilet "burps" over and over. The water remains clear, although there is a faint sewer smell. Typically once done, the water level in the toilet is then very low as if it's been sucked out.
The first flush doesn't work well, but the second does normally.
There is a single studer (I think that's the spelling) vent for the basement bathroom - I think the PVC is about 2 inches. I told a plumber about this exact issue when we were having our basement finished in the area, so he replaced the original (same) studer with a new one. He also ran the PVC up inside the wall higher near a tray in the ceiling so it could breath in the open void (which is not airtight and open to a storage room).
There is a shower, a sink and a wetbar all using the same bathroom drain but those are seldom used. I occasionally run them to wet the traps.
There is the exact size studer vent off my main house drain line. I'm not aware of any vent out the roof and don't believe there is one.
So what is causing this burping? I've got a few ideas - help me choose the right answer:
1. Since the water level is drawn down most times, I feel as if the air in that bathroom drain is getting pulled. Since this happens, for instance, when someone showers or flushes above, I think water rushing in the main drain past where the basement drain meets it is creating suction - "pulling" on that air in the basement drain pipe - and finally getting it by taking a breath out the basement toilet - creating the burps.
If that basement bathroom studer was doing it's job - the system would suck air from it vs. from the toilet. So it's faulty or simply undersized. I wonder why, however, it couldn't get "breath" from the sink/shower/wetbar - I'd think water in their traps would be easier to pull than the whole toilet's water.
In this scenario, even if the whole house has a strong, working vent somewhere, if a solid core of water was in fact rushing past the basement bathroom drain junction, the whole-house vent wouldn't even be a factor - a vaccum would be created in that basement drain regardless.
2. I consider that perhaps this isn't a venting issue. Perhaps the septic is somehow failing and the main-house drainwater tries to get out into the septic but is stopped - so instead makes a right turn and begins to flow up the basement bathroom drain - pushing the air out the toilet (vs. pulling in my example above).
Yet I haven't experienced any dirty water in the toilet - and this problem has been ongoing for a long time now. I do, however, smell faint sewage when it burps - but perhaps this is only due to the fact that there is a momentary opening between the bathroom drain and the room.
4. My final consideration is that perhaps I have a "slow" septic, and it in fact can't handle a rush of water at once - and house water does in fact flow up the bathroom drain enough to cause the burps - yet luckily recedes before water actually reaches that toilet and enters the room. So I'm dodging a stinky mess on a daily basis. Some neighbors report never having their tanks emptied in 12 years and during times of heavy use or wet ground, their systems "slow" and don't work well until the water purges off (some say our area soil isn't great). Septic "experts" would tell them they needed replacement yet they'd delay - only to have a still-working system years later that they simply had to be cautious not to flood - a "tip" most septic experts recommend anyway.
I'd love to get a consensus on what I can do here or where my problem might be.
These "burps" are loud and splash water. Unfortunately, my wife was sitting down when they happened earlier. So now I'm on the hot seat!
Perhaps there is a vent after the "sink/shower/wetbar", then past there no vent. And the falling water is first "pushing" the water in the toilet with pressure, then the smell comes out. Then it falls past that point and then sucks the water out of the toilet???
And maybe with a large pipe to the septic tank, water would flow in the lower portion of the pipe. And vent air would flow in the opposite direction (normally)?
But what if there was a bunch of "goop" in that big pipe going to the septic tank, say filling the lower 1/2 of that pipe? Then water could only flow in the top half, but no vent air could travel in the top half...
So perhaps get one of those sewer camera gizmos and peek in the pipes and see what is going on where. Where vents are and so forth. If goop in pipe or septic tank needs to be cleaned out.
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