Thanks for your suggestions everybody.
I've put an old bath plug over the pipe top to try to confirm that the overflow pipe is the culprit. I'll try to get hold of one of those sight glass thingummyjigs. Is that the technical term I should use when searching plumbing merchants?
Mmmmmmm, our walls are 3 ft thick stone. I guess this is why the lazy plumber didn't bother in the first place!
Does anybody know of some sort of filter I could cap it with before I bring in the demolition mob? Obviously it would need to let overflow water out if necessary. (Hence why I...
Help! I have been reading all the other listings that relate to this problem. I think I have sewer gas getting into 1 of my bathrooms. (1st floor)
The smell doesn't seem to be escaping from the traps or toilet u-bend and there is no sucking or obvious draining of these either. It seems to...