Actually I've just realised I'm barking up the wrong tree anyway.
There is a major foul drain smell coming into the house, mainly into the bottom floor of a 3 storey house. Sometimes it's fine, sometimes it's really bad.
This particular internal soil pipe only serves the very top floor for a bath, shower and toilet.
My initial thoughts were a blocked vent pipe but then there would be a vacuum on the facilities connected and the smell would be on the top floor. That isn't happening. They are also draining fine - no overflowing etc.
The only thing I can think of now is that the vertical soil pipe has been damaged somwhere and gases are coming out there. Having removed some of the boxing in I would expect water to also trickle out of any compromised part of the pipe and end up at the ground floor. Again, that isn't happening.
Do you know what the stack and underground drains are made from? If all plastic then unlikely to have a broken joint, but if underground drain is clayware, then it's not unknown for slight ground movement to cause the drain to crack where the stack joins, if not elsewhere too.
The stack is plastic but the underground piping is clay. Where it connects in the concrete floor the concrete seal is intact. There is some moisture in the ground area there which is more evident from the stained ply housing which sits on the ground but nothing untoward.
Chris, would the blocked vent cause the smell though?
Smoke test might be the way forward then, will indicate any breaks/leaks inside the building. Can you get access to inspect the stack inside the house? May be a redundant connection still open somewhere on the stack.
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