Sewer smell

64pvolvo1800

I am on septic at my cabin and I built the home about six years ago. Big cabin and very little traffic, so the tank is probably not full. There's never been a backup at all. The trouble I have is a sewer smell in the second floor of three. I narrowed it down to one area and I suspect a pipe which I believe it a wet vent because it carries the sewage from a third floor toilet down a wall to catch the main drain along with venting to the attic vent.
I've opened up the ceiling below it and inspected the piping with a camera all along the outside but it drops into an exterior wall with insulation and I cannot see anything without opening the wall.

My plumber who installed it new says he can put a 4" trap just outside the house by the clean out and it will trap the smells and fix the problem.
I have zero sewage leak anywhere, and I suspect I have a screw in the vertical pipe somewhere.

Question is: will it fix the smell and is there any real reason to chase the problem in the house?

joecaption

Well there's your problum, there's a dead cat behind the wall. Must have dehydrated from no one flushing the toilet up stairs.
Are you 100% sure it not just a dry trap from lack of water being used or a leaking wax ring under the toilet?
I like to try the cheak easy stuff before ripping out walls.
All I can see a trap install outside doing is causing the whole thing to back up from a blockage much faster.

64pvolvo1800

Three showers, two garden tubs, eight sinks, five toilets, washer, dishwasher, no ac drains into sewer out of three ac's.
Positive it's not a dry trap, ac, wax ring, etc as I have addressed all these things already. It's most certainly coming from this one chase but I'm not really anxious to rip out drywall if a simple trap will fix it. I rent the cabin out these days from time to time and certainly don't want to kill anybody with gas. On the other hand, licensed plumber is telling me he does this elsewhere and guarantees it will fix it. 4" trap in 3" line with dual clean outs. Before and after.

joecaption

I'm hoping some of the full time plumbers will hop in here and suggest something.

Nailbags

So your going to put a wet trap in? this is a part time home used only summers etc? if it is a wet trap you know water has to run in to it 24/7 right? what it sound to me is you have illegal s trap or a siphon going on in one of your traps. were it is still wet but not closing off.

64pvolvo1800

First, NO, I am not going to do anything! My licensed plumber proposed the trap outside the house. I used the term wet trap initially referring to the drain/vent from the third floor toilet going past the second floor toilet and also providing a vent. I'm bit a plumber and so I probably am not describing it correctly.
The problem surfaced in the last few months and there have been no changes in the system since new.
No illegal S traps and no dry traps so no siphon either. I really suspect a screw that hit a vent and is now rusted out providing an escape path for gas.

COLDIRON

You mention the problem just started a couple months ago and you suspect a screw in the pipe.
That tells me you know something we don't so go to the area where you suspect the screw causing the problem and start digging through that wall uintil you find it. Sounds like you or someone else was hanging pictures or installed something on the wall of the area in question.

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64pvolvo1800

No, I have no clue and have not hung anything recently but the plumber said its common for this type of problem to occur as a result OF such a thing. Believ me, if I had any thought of a recent hanging causing this, I'd have already camera inspected the wall to see and confirm and fix it.
Plumber just says we can go through many walls before identifying a possible drywall screw being the offender!

I do appreciate the suggestions and I'm hoping someone will have had a similar issue and point out the magic bullet or magic pill! I watched from afar on the PZ pro website and the search also suggested a screw has been very often the culprit.

I guess I'm more interested if having the trap immediately outside the house by the c/o will be a solution and or an issue. Note, my septic tank is about 50 feet lower in elevation and 2-300' away from the house since its in the mountains of Tn. Like I said, never any problem with anything since new until now.

TheEplumber

House traps have been illegal in my area for a long time.
Do a smoke test.

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Javiles

I am With E get the system smoke tested no guessing if its sewer gas you'll know it and see where its coming from.

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ben's plumbing

yep smoke test will tell the truth .. no guessing....ben sr