Hole in concrete floor below kitchen sink unit?

7 Dec 2023
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United Kingdom
Hi all

I've been trying to find the source of a cold draft in my kitchen after taking off the plinth below my sink I have found a hole in the concrete floor (where the cold air is coming from), and it has a pipe going into it. I have a few questions...

1. Does anyone know what this pipe is? I think the white pipe next to it going into the ground is the drain, could this be cold water feed? The stopcock is above this at the back of the unit, but think that has copper pipe? (I have no idea about plumbing so this may be a silly question)
2. Can i fill the hole in to stop the draft? Expanding foam?
3. I have also noticed there is a lot of what looks like condensation build up on the pipes in this area, so much so that it is actually dripping onto the floor. Is this as a result of the cold air coming up from the hole? Should this go if i fill the hole in? Anything else i should be worried about?

See photos



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Ok thanks - expanding foam okay? And by joint i assume you mean up to the blue nut that's in line with the floor? Do you also think this is the cause of the excess condensation on the surrounding pipes?
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