Upstairs bathroom... double cabinet... double sink. Only the attic is above this bathroom. No order in any other bathroom or any where else in the house.

In our upstairs bathroom there is a strong septic smell only after I've had a long shower. There is a slight odor underneath one cabinet only... the other cabinet smells perfectly fine. We had a plumber in and found out our toilet was properly sealed so that was fixed. That fixed a part of the problem. The smell under one sink continues. When the water is not running the smell goes away. If you run the water a little bit there is a little bit of an odor but not much. A long shower will produce a pretty icky smell. No foul air around tub or shower or toilet... only underneath that one cabinet!

Any suggestions?? Advise?

It sounds like the vent itself is not working well. When the sink is run and that waste line is not venting well that could create a back gas to escape from the vent pipe to release a small enough of sewer gas out of the sink overflow and or drain.
How well does the sink tub and toilet drain? If this is slow or getting slower the vent is getting clogged some what or there is a partial block age. Since its under the sink where the trap is check the trap to see if its loose in the back into the connection. If its slightly buried in the wall and the top and the top of the connection is not 100% sealed gases could escape from there but yet the sink not leak. Check connection under sink first.
How long has the sink smelled aside from the toilet?
Three basic for sewer smell
The waste and overflew in tub and sinks have microbes to make the smell and when we run the water the waste and overflow pushes a little air through that and the smell gets heavier.
The vent is clogged and the drainage is letting gases vent through the waste and overflow.
A sewer line is cracked to drain that bathroom and the crack is high enough to let sewer Gauss escape.
Check waste and overflows in sink and bathtub.
Check trap connection from sink and for ant tiny leaks.
Did you have a ice storm or a big snow that could clog your roof vent or a tree right over the roof vent?

Signed 21 Boat

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Thank you so much for your answer. Some of it is a bit greek to me though I must confess.

The smell has been there for about 2.5 years! I keep thinking we've fixed it and alas we have not. The sink and tub and shower all drain well... no changes... no slow drainage. The toilet does not flush well at all but the plumber says it's because it's a cheap toilet, water saving toilet etc. He says the toilet is not the problem. Where is the vent? Got to like questions like that don't you:) I had the plumber check the pipes under the sink as far as he could see... all is well... BUT... things were not sealed and he sealed them as far back as he could see. The plumber asked me to check the attic the next time there was a strong smell to see if it was also in the attic. So far, the only place I can smell anything is under the one cabinet... the smell doesn't even drift into the other cabinet which is amazing to me.

No trees around the roof vent. Roof vent was replaced when we redid the roof. At that time there was a terrible septic smell outside. The roof vent was moved as they told us it was too close to the edge of the roof. The bathroom that smells is the one right under the roof vent. The only thing between the bathroom and the roof is gyproc and insulated air space.

I put my hand all around the pipe under the counter and nothing is wet as far as my hand/arm can reach.

Would putting some javex down the drain help at all? You can see that I am truly a newbie at this.

The upstairs bathroom is linked to the kitchen, 1/2 bath and lower bathroom and none of those smell... it's just the one upstairs.

The plumber says he really doesn't know what to think and of course wants to start taking out gyprock... sure wish I had more confidence in him.

Thanks 21 Boat
D.

Things were not sealed meant there was a leak. Can you explain that better. A leak not sealed is a place for gas to escape
If the smell was in the sink its self and was in the bowl area I would say it's the waste and overflow. The part that drains the sink if the water stays on and the drain plug is in the holes underneath the faucet in the bowl

Lets at least do a cheap experiment before the wall Plug up the sink and fill it half bleach and half with hot waste. Pull drain and let it go all at once. I would do this twice. If this helps knock down or stop for a while the oder than it proves that its in that drain system. I I wanted you to do it twice so if there is a little leak back in the wall the bleach will help some what of a small sewer leak of liquids.

My next alternative is to get into the wall under the sink and cut the drywall out there and look and smell to chase it. If the vanity has a full back the then some valve issues needs address. You cab call a second plummer for another opinion
See how the bleach goes. And recheck the waste and overflow on the sink

Signed 21 Boat

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Thank you. Will do the bleach thing once tonight and once tomorrow morning. I'll see how that goes and write to you again letting you know the results. You are a kind person answering these questions... I really appreciate it.

D.

Things were not sealed meant there was a leak.

When the plumber looked at the pipes they were not glued together so he glued them. He said there wasn't a leak but whoever had installed the piping had not glued the pipe fittings. So he went back as far as he could and glued all piped without taking a lot of gyprock off. We repaired the bathroom for the 2nd time!!

What do you mean half bleach and half hot waste.............and plug up the sink. Not exactly sure what you mean. What kind of waste??


Can you explain that better. A leak not sealed is a place for gas to escape
If the smell was in the sink its self and was in the bowl area I would say it's the waste and overflow. The part that drains the sink if the water stays on and the drain plug is in the holes underneath the faucet in the bowl

Lets at least do a cheap experiment before the wall Plug up the sink and fill it half bleach and half with hot waste. Pull drain and let it go all at once. I would do this twice. If this helps knock down or stop for a while the oder than it proves that its in that drain system. I I wanted you to do it twice so if there is a little leak back in the wall the bleach will help some what of a small sewer leak of liquids.

My next alternative is to get into the wall under the sink and cut the drywall out there and look and smell to chase it. If the vanity has a full back the then some valve issues needs address. You cab call a second plummer for another opinion
See how the bleach goes. And recheck the waste and overflow on the sink

Signed 21 Boat

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Sorry close the drain on the sink Now pour half the sink with bleach and the other half with hot water now release the drain all at once.
This should help get rid of the smell for a couple of days especially what I just read of pipes not being glued.
Its just about guarantee there is a small leak further back in the pipes. Not all small leaks show up in the house. So try rhos and if that stop's some smell it's a leak in pipes because the bleach will kill some of the leak smell

Signed 21 Boat

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In my experience, if you know the trap arm piping is sealed and you're not getting a smell from inside the sink itself (from the vent hole or the drain), then your problem is in the drainage/vent piping in the wall.

Sometimes, the vent piping isn't all the way in the drainage tee in the wall. Also, it's possible the vertical piping coming out of the bottom of the tee may not be sealed. Or the line may be split in place.

Either way, it's a fair bet that your problem is at the wall.

The evidence is that it is in one cabinet and not the other.

Drywall is cheap to repair, however, the longer you allow this "smell" to go on unchecked, it could make the air in your home sick which has proven to cause health problems.

Not to alarm you, but, the Asian SARS virus was caused by similar conditions.

I would suggest resolving this issue as fast as you can.

I have used 1/2 bleach and 1/2 hot water two days ago as advised... so far no septic smell. Well that's just too good to be true! :)

Wouldn't it be nice if that solved the problem somehow. There's been lots of hot showers and running water since I did that and so far all is well.

I'll write again and let you know the results. Thank you ++++

I have a septic system and only when it rains do I smell gas from the system. The toilet was removed and a new heavy duty wax ring with plastic extension applied. After resetting the tank, I sealed allarounf the bottom of the tank with a caulk and let dry. There is no odor with the sink or shower or even the washer drain pipe. The smell only becomes noticeable when heavy rains come. The toilet flushes well and the sink and shower drain well. The smell seems strong when you smell near the ceramic tile and where the base sits.
Thanks in advance for any help.

Jim S.