Why the smell?

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We’re getting a really bad urine smell coming from under our ensuite sink and I wondered if anyone could help me work out why and where the issue is so I can look at sorting it.

I’ve taken off the vanity unity underneath to eliminate any issue there. The reason for taking it off was every time we opened it the smell was overwhelmingly worse.

I’ve also taken the basin trap off and blocked it with a carrier bag to check it’s not coming from there, and it’s not.

It seems that the smell is coming from the gaps around the waste pipe and it’s worse when there’s a breeze outside.

I haven’t noticed any leaks anywhere or any signs of leaks on the ceilings below either.

Any tips/suggestions for how I work out what’s causing it and then if there’s a way I can make the waste pipe better as it currently doesn’t have much fall and takes up a lot space under the basin. And a proper MacAlpine fitting too for a trap.

Photo attached. I’ll try to add a photo of the outside soil stack and how it’s been setup by the previous owners in a bit.

Thanks everyone.
 

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Could the smell be from outside? How is the soil pipe vented, AAV or a pipe going up above the eaves?
 
Does these outside pics help?

(left is shower outlet, middle is sink and right is bath)
 

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Check that a trap isn’t being pulled, eg when you flush the toilet, or when you’re emptying the bath, or whatever is connected to it.
 
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Check that a trap isn’t being pulled, eg when you flush the toilet, or when you’re emptying the bath, or whatever is connected to it.

The sink trap? If so, it’s always got water in it so I’m guessing no is the answer.

I’m 99% sure the small comes through the gap around the basin outlet gaps in the wall if that helps.
 
Open vented! Any chance the smell might be coming back in from that open vent in the third photo, when the wind blows a certain way?

hmmmm. So when we first moved in it didn’t do. It only the last year or so it’s been driving us crazy. Very strange. If it was an issue with the stack would it not be coming out of the waste pipe rather than the hole in the wall?
 
Open vented! Any chance the smell might be coming back in from that open vent in the third photo, when the wind blows a certain way?
Bit of a stretch, it looks more than the 0.9m above an open window height.
 
There’s a fitting fitted upside down as well.
 
It may be the join between the toilet and the pipe, the hidden bits behind it.
Maybe you need to consider removing the toilet and getting access to the short run to the stack?
See if there is pee there.
 
hmmmm. So when we first moved in it didn’t do. It only the last year or so it’s been driving us crazy. Very strange. If it was an issue with the stack would it not be coming out of the waste pipe rather than the hole in the wall?

Check the manhole, in the ground, where the soil pipe discharges to - make sure that is clear, flush the toilet, run the tap, make sure the flow drains quickly and completely down in and through the manhole. Check there are no pipes leaking into the cavity, finally - seal around the pipe where it passes through the wall.

If it's any consolation, we have the same issue in the downstairs toilet and I have never been able to trace it. It is so irregular, appearing no more than once per annum. I've had the toilet out twice and the wash basin three times trying to find the source. There is no vent, the toilet discharge goes straight down, washbasin into a hopper, then both into a manhole in the drive just two feet away. Once per year, I give the hopper in the ground a good flush out with hot water, which seems to alleviate it.
 
Under the basin doesn’t look too good does it? The outlet should be lower than it currently is wouldn’t you say? Maybe it’s worth redoing it but that’ll involve cutting a new hole or moving the brick wont it? The porcelain tiles inside won’t be easy to cut either will they?
 

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