Sewer smell, smoke test yielded nothing, what now?

First thank you everyone who could help.

Let me start by saying I've read quite some on the subject and know about the need for p-traps, their tendency to dry over time if not used or during the winter, the clogged vents preventing air from coming in when water flushes down and/or sucking water out of p-traps etc.

Not to brag, of course, just trying to cut to the chase if possible.

The problem is this: we have a sewer smell in the office when next suite (commercial kitchen) is operating. If they do not operate we're good.

After eliminating AC as a source (it definitely contributes to moving the smell around though as there are both grills and return in the room) we ended up calling a pro who did smoke the building to no avail.

He said the 4 vents at the roof were puffing like canons and if he had increased pressure gas would have started to come out of sinks.

SO long story short the smoke did NOT help find the source. He smoked from the top and also from the bottom - where the city pipe enters the building and at the grease trap (not sure why or where - probably after it).

Same nothing.

My question, which he unfortunately failed to answer, is what is next?

I am trying to figure out how is it possible for gas to get to us reliably when kitchen operates and then not when smoked.

One thing I am missing so far is the knowledge of what exactly triggers it. Tried filling the 3-compartment sink in the kitchen and releasing them together and didn't get any smell.

thats weird, i have only tested using smoke after i capped the vents on the roof.and plugged the sewer and traps.



little common sense please.

you have a pipe with a crack, hole, in it, you want to find the crack/hole
so you choose to use smoke to find it.
do you...

1, smoke the pipe with both ends open. watch the pretty smoke as it leaves the pipe on both ends
2, smoke the pipe with 1 end open. watch the pretty smoke as it leaves the pipe on one end
3, cap pipe openings and watch for smoke
4, buy a case of lysol spray

Every smoke test I have done is with a closed system.

johnjh2o said:

Every smoke test I have done is with a closed system.

Click to expand...

thanks John,
sounds like his test guy srcewed the pooch on the test.

you have to have a little pressure to "make" the smoke go where it does not want to go

I have a little story that goes with a smoke test I did. I was doing it from the roof on a small building. Next door was a apt. complex. I happened to look over at the apt.complex and I see smoke coming out of the vents on there roof. As it turned out both buildings were on the same lift station. I guess they didn't have any sewer gas leaks or I would have seen fire trucks pulling up to the building.

not smoke related, i was digging a sewer line, out the corner of my eye a see the next door neighbors electric meter smoke and wiggle

LOL OPPS!!!!....

or. pulled up to a house with the back hoe on a trailer. and see about 500' or more cable tv wire behind me. LOL OPPS !!

frodo said:

thats weird, i have only tested using smoke after i capped the vents on the roof.and plugged the sewer and traps.

Click to expand...

I do not mean to argue here.

My common sense says that if odor is being pushed out when the system is normally used , i.e. without closed vents on top, then it should be able to produce the same result under the same conditions when another gas is pressured in.

Why wouldn't it?


Besides, leaving the vents open allows for observation of whether some of them may not be clogged and releasing less than others. This was not the case.

I'll give the guy a call today, but from what I saw of him I think he knew his trade...at any rate better than I do.

I had one of these, actually a couple. One time the sewer smell only happened when the wash rack wash in use (commercial building- bus garage), the first test failed. I pressed the service into repeating...roof vents should be closed or its not going to work. Second time more smoke was used and we watched longer. after quite a while- smoke filled the ladies restroom....it was still hard to tell from where, but we determined it was a block wall- we had to knock out the block...sure enough, and old 2 inch cast iron cross (part of vent system) had a dime size hole rusted through the back of the fitting, we could not see it, but I felt it, my finger fit into it!
That was a hard fitting to locate a replacement, but we did, it fixed the issue.
Plug those roof vents, do it again, and give it time!

kolevbg said:

I do not mean to argue here.

My common sense says that if odor is being pushed out when the system is normally used , i.e. without closed vents on top, then it should be able to produce the same result under the same conditions when another gas is pressured in.

Why wouldn't it?


Besides, leaving the vents open allows for observation of whether some of them may not be clogged and releasing less than others. This was not the case.

I'll give the guy a call today, but from what I saw of him I think he knew his trade...at any rate better than I do.

Click to expand...

When water is rushing into your drains it is displacing some air and causing some pressure to build or be moved around. The smoke test is not the same unless you plug the openings.

Talked to the plumber today.

He backed up his decision to blow the system with the vents and said that it's all a matter of the size.

With building this small, he said, (about 7000 sqft) and the type of machine he uses, if he closes the vents it's guaranteed to blow through the p-traps.

So it is one expert's word against another.

But I am in a service business myself and know first hand there's never just one universal truth.

What pickngrin says above about same situation and giving it more time makes sense.

What would be a reasonable price I should pay for that and should I try doing it myself?

First time I paid around $1400 . I do not have problem paying them again if i knew I'd get some definite answer.

Trying it on my own gives me the freedom to try until it works, but it also has so many opportunities for me to screw that I am not aware of...not sure if I should try.

/.......................

kolevbg said:

Talked to the plumber today.

He backed up his decision to blow the system with the vents and said that it's all a matter of the size.

With building this small, he said, (about 7000 sqft) and the type of machine he uses, if he closes the vents it's guaranteed to blow through the p-traps.

then plug the p trap, JEEEZ....this is not brain surgury,
A 4 dollar plug, or cap. disconnect the trap, cap it
pull the toilet, plug it

I hate a lazy SOB.




So it is one expert's word against another.

But I am in a service business myself and know first hand there's never just one universal truth.

What pickngrin says above about same situation and giving it more time makes sense.

What would be a reasonable price I should pay for that and should I try doing it myself?

First time I paid around $1400 . I do not have problem paying them again if i knew I'd get some definite answer.

Trying it on my own gives me the freedom to try until it works, but it also has so many opportunities for me to screw that I am not aware of...not sure if I should try.

Click to expand...

here is what you need to plug the drain




in case you need to hold it down

Hehe...appreciate the humor with the brick

Do you recommend taping all existing outlets / fixtures then?
(pardon my home-depotian if you can)

Following the logic then apparently yes, I'd need to plug everything.

I'll sleep over that.

Thank you for sticking with me.

With exactly zero first hand experience and based on the symptoms I get I am leaning towards a theory that a crack inside or under the foundation is leaking water and, of course, once the water source stops and the pool gets sucked into the soil it leaves a smelly air gap.

When running water starts filling the hole in the ground again it compresses the air gap pushing it up. Part of that air finds its way through the foundation and into the building.

Does that sound credible? Personally I can't imagine how it would go through the foundation without it being cracked and then how it goes through the floor, but that's the best I could come up with.

Such a theory would explain why the gas test failed (would need lots of gas/pressure to start moving other gas/pressure whereas water will do it more easily), also would explain why it takes time before smell starts (at least I've tried to flush the 3 compartment sink once to no effect on the smell) and lastly would explain why we're having trouble finding the source of the smell once it starts.

So how does it sound? And if it is correct and I do the test with closed system and wait for long enough would I still see dark gas coming out of the wall or floor cracks?