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Discuss Can't get rid of the smell of gas sewerage leak, under my kitchen sink. in the Plumbing Forum | Plumbing Advice area at

There is no smell coming out of my sink plughole, never has been.
There are no water leaks in the piping and U-bend under my sink.
Have tried on several occasions using very strong drain un-blocker and odour remover, to remove smell, but has not worked.
Sink plughole never blocks up and water runs freely and quickly through plughole.
Sewerage gas smell, seems to come from both threads/nuts at both ends of U-bend and the thread/nut where it joins the waste pipe and finally another thread/nut on the waste pipe, where the pipe disappears through kitchen cupboard and into the cavity wall.
I live in a first floor flat, above me is another flat, with the kitchen directly above me.
Below me is the ground floor and I'm directly above their bathroom/toilet.
The main waste pipe is in the cavity wall behind my kitchen cabinet, which runs from upstairs down to the ground floor and joins the sewer I presume.
The upstairs flat experience no smell in their kitchen or bathroom whatsoever.
Plus the downstairs flat also experience no smell in their bathroom/toilet and kitchen.
This has been going on constantly all this year and sometimes despite the kitchen cupboard under the sink, with the door firmly closed the smell of sewerage is over-powering.
Hope you can kindly advise me what to do.
I'm on low income, an old age pensioner and rent my flat privately.
Unfortunately landlord simply suggested that I try using baking powder and white vinegar to remove smell.
So far this has been unsuccessfully.
What would you advise me to tell my landlord how to fix it himself.
As I feel he is reluctant to use the services of a professional plumber.
I look forward to everyone's reply.
Thank you kindly in advance for all your help and support now.
Hi gpbeck,
Thanks for your suggestion...have now attached 2 photos, of all plumbing under my sink.
Further information, never had a problem in all of 13 years, with the same plumbing, until this year.
Never use the washing machine, as a friend does all my laundry.
However to see if I could fix my problem. I ran the washng machine last week. Next day, there was a NEW foul smell (and not coming from under my kitchen sink, but around and underneath my washing machine) but not of leaking sewerage gas. Landlord's workmen, promptly arrived, discovered that the waste pipe on my washing machine must have come loose after I did the ONE wash. They duly fixed it and immeadiately "the NEW foul smell" disappeared and fortunately has not returned.
Still persevering each day, using baking soda and white vinegar down plug hole and leaving, then rinsing with hot water, but still no improvement with the constant smell of sewerage gas, under my kitchen sink and in the cupboard.
Just to reiterate, I have had this smell of sewerage gas, underneath my kitchen, consistently for 6 months.
Further information, my landlord owns his own building company (20 years)
Plumbing1.jpgPlumbing2.jpg and built my block of flats and many, many more houses, etc. So I presume he must know a lot about everything involved in the whole plumbing process of a building, etc.
Hope the photos are of assistance now.
The basic layout looks ok. I don’t think vinegar etc will ever do anything if there is a significant blockage. I think good start would be to disassemble the white pipes (white collars should only be hand tight), see if they need cleaning internally as may have sludged up. U bend will have contents so put basin beneath.
Hi gpbeck,
Thanks for your reply. The workmen have already disassembled the white pipes, said they were ok. But agreed strong bad smell coming from waste pipe. Then they assembled again and just left, saying they would report back to landlord. The landlord did try to blind me with science, after they fixed my washing machine and said re underneath my sink "that there was an air bubble and it was all to do with the pressure of water and would all be ok in a couple of days"
His workmen, disassembled the white pipes, the day after, what the landlord told me.
His wife who helps run his business and takes the majority of enquires, messages, etc...said she would look for solution on the internet...hence getting back to me about baking soda/ really at a loss and quite exasperated unfortunately....wondering where I go from here?
If all those white drain pipes are clean and assembled correctly they will be sealed, water and odour proof. The smell is therefore probably coming from behind or under the unit but not those pipes.


The bottom line is that under normal pressures encountered within waste pipes and fittings, they are essentially gas tight. If you can smell gasses they are also normally leaking water during use. You would surely notice water escapes no matter how small during your investigations. It's not impossible for gasses to leak where water cannot but it's highly unlikely.

I can only suggest replacing all the rubber seals in the fittings, just in case, and seeing if the smell persists. In the absence of fresh seals I would disassemble and wrap all seals with a couple of wraps of PTFE tape. That's a bit of a bodge in place of new seals but sometimes needs must.

Just to be absolutely clear, the smell is coming through the pipework and definitely not out through the waste inlets/plugholes?

I would be starting to suspect another source for the smell. More than once I have found an open end or a boss connection unused and without a cap or plug. Sometimes in hidden places.

It might be worth getting a camera probe with built in light behind those units to see what's up. Some plumbers carry them and they are surprisingly cheap nowadays if you need to buy one.
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Gas Engineer
Personally I think your smell could be stagnant water coming from that massive loop in your overflow pipe (black corrugated pipe). However that would normally be a smell in the kitchen sink area as opposed to under it. Could be smell from behind cupboards as suggested.
Hi guys and to all of you, that have replied.
Re... Stigster....smell definitely not coming up through plughole. I hear what you say about hidden places and what could be lurking behind my unit. Will if necessary, push my landlord and workmen to explore there. Thank you.
Re....gpbeck and Aquarius....Thanks. tend to agree with you and have thought this for some time. There is nothing under the unit and no smell. Back of the unit is against plastered brick wall and cavity, where waste pipe from my kitchen, joins waste pipe from upstairs kitchen, that comes down past my flat to ground floor flat, to their bathroom and out.
Workman last friday, when he disassembled all white pipes, told me there was a real bad stink coming from my waste pipe that leads out into the cavity in the wall and connects up with piping, I presume from upstairs and downstairs.
In my ignorance I could be well be wrong, but that is where I believe, the really bad stink (like sewerage gas) is coming from.
After the weekend, I intend to ask my landlord and his workmen to replace all my white pipes and waste pipe, with all new pipes, with all new seals, etc...this way eliminating any defects, etc...all the current plumbing, I have had no problems, whatsoever for 13 trust the workmen to assemble everything correctly.
Then if problem persists, think it will become quite evident, that the smell is coming from behind my cupboard and
that is hole in back of my cupboard, where my waste pipe goes out of my flat and into building cavity wall and joining other piping!!.
Many thanks to you all guys, for your ongoing support, ideas and assistance, it really is appreciated.
Whereby as regards, all that I've just said, please do correct me and put me straight, if I'm way off the mark here and what I'm thinking.
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Hi Guys,
Trying my best to use a process of elimination here, so here goes. Remember I've had no problems at all for 13 years with my current plumbing, ok.
(1) No smell of any kind comes up through my plughole, so that rules out overflow pipe (black corrugated pipe)
(2) Remember I never use my washing machine, but did last week, but workmen fixed that and totally eliminated the NEW SMELL problem, caused by washing machine (scroll back through my earlier posts if necessary, thank you).
So think that eliminates, all pipes to do with my washing machine.
(3) Which only leaves white pipes and waste pipe going out of my flat, somewhere?
(4) If all white pipes are replaced and fitted properly, plus new waste pipe and fitted properly, going out of my flat somewhere? (where ever)
(5) I can only deduce, where ever my waste pipe goes out of my flat, the smell comes back in through my waste pipe from where ever?
(6) The "where ever" being. Would my waste pipe, be connected up to the upstairs flat and their waste pipe (from their kitchen, which is above me) and pass my middle floor flat (in what I call the hidden cavity wall) to connect up with the ground floor waste pipe in their toilet and bathroom, that is beneath me?
(7) And where does this waste pipe eventually go from there, I presume next stop is the sewer.
(8) Only problem with my theory is, both upstairs and downstairs flats, have assured me that they, have not got any bad smell in their kitchen (above me) or bathroom (below me).
Thank you kindly guys, for all your ongoing support, help and patience with me!! Really appreciated.
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Only other thought being, with the constant smell of what seems to me, to be like sewerage gas, could the SVP Soil Ventilation Pipe in the building be clogged up?
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I had a similar problem once and tried everything I could think of before I realised that the ‘CONDENSATE’ pipe from the Combi boiler had been gravity fed into a vertical waste pipe going in to the pipework under the sink but WITHOUT any u-bend The smell was due to there being no water seal via a u-bend trap for the vertical pipe. Because of this back pressure of gas from the drains was coming back up around the condensate pipe. To avoid re-Plumbing I simply packed around the smaller condensate pipe with a plastic bag. This sealed the arrangement. No more smell. Check to see if the white plastic condensate pipe 22mm is doing something similar. I can’t see anything like this actually in your photo but Just a thought..
Hi Mdljk, thank you kindly for your reply, really appreciated. Next time I see the workmen, I'll definitely mention this. Glad you managed to finally resolve your problem.


Gas Engineer
Mk1 human nostril... you need to sniff out the source. Go all over the room high and low level, inside and under cupboards etc.
Hi WC1, thanks for your reply, just when I think I've more or less pinned down the source, it seems to jump about, but on the whole, I think I'm getting closer. Used to think, that it was coming from behind the cupboard. But now it seems to be coming from both seals on the U-bend and occasionally outside the cupboard, at the same level as my head.
Disconnect the U-bend and remove any stagnant water remaining in the sink overflow and washing machine waste pipe. Buy a 40mm compression blanking cap and fit it on the pipe coming out of the wall. Ventilate the kitchen and wait to see if the smell returns. If the smell is still there then it must be a leaky pipe in the wall cavity.
Hi Dan 1990, many thanks for your informative reply, in my little knowledge, all that you say, sounds very logical and a good way of eliminating and narrowing down the problem.
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Thanks Mdljk
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Last time I had this problem I traced it to a large hole, gnawed by a rat, in the 1 1/2” as it passed through the cavity wall to outside and into soil stack. This was on top of the pipe and so very rarely leaked.
Hi Ben-gee, thanks for your reply, can't pretend this thought has already run through my head. Can only hope my landlord, tells his workmen to do a thorough investigation, next time they visit, as all this is totally knew to me and the more I learn, I realise the less I know!!


Another time a nasty drain smell turned out to be 1/2 lb of mince beef put into a microwave to defrost and forgotten about!

That I traced with my considerable hooter, when I opened the door I gagged and my eyes were watering...f**kwit tax had to be added to that job.


Gas Engineer
Another time a nasty drain smell turned out to be 1/2 lb of mince beef put into a microwave to defrost and forgotten about!

That I traced with my considerable hooter, when I opened the door I gagged and my eyes were watering...f**kwit tax had to be added to that job.

Was there all kinds growing on it as well? 🤢🤢🤢
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WOW!!..Unbelievable, but so true, eh!!..Fortunately I'm not that stupid, but some friends of mine, would say that's debateable, lol.
Good news!!....continuing to use baking powder and white vinegar the last few days. Finally the smell has gone completely.
Many thanks for all your patience, help and support, whilst I was trying to get this problem resolved, it really was appreciated. stay safe.

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