ianw wrote:
periodically we experience a foul smell in the bathroom (not just after
a recent visit!)
I suspect the soil connection to the wc pan
the current connection appears to be clay (?) wrapped in some kind of
bandage which dissappears horizontally into the wall.
The exterior stack is cast iron.
the clay pipe is obviously very old and does not even have a circular
cross section any more (but there are no signs of a leak this side of
the wall)
Would a new plastic pipe with rubber flange simply push-fit into the
cleaned-up cast iron?
Could the smell be caused by a blockage in the top of the soil stack
(birds nest etc)?

The house is a two storey stone building of 100+ years

Many thanks,
Ian
Perthshire

I suspect that one or more U-bend traps is being sucked dry. Possibly in
periods of high wind.

Sniff at the plugholes next time it happens

It could be simply bad design or a blocked vent.

It may be possible to install a Durgo type air admittance valve into the
pipework if it is bad design.