Christian McArdle wrote:
When water from the (upstairs) bathroom shower or sink is released into
the grid outside the kitchen, a noxious, sulphur/garbagey smell
overwhelms the kitchen and part of the living room.


You might have an unused trap that has evaporated out due to non-use. This
could be for a washing machine (that was later moved into a separate
utility, for example) or a water softener that the previous residents took
with them.

If so, the fix is to either refill the trap manually every month or two, or
to remove the trap altogether.

Surely that would only be the case of the upstairs bathroom was only
ever used once in a blue moon; presumably the OP uses it more than that?


Isn't it just going to be something nasty in the gully outside? Maybe
whatever is causing the pong only does so when there's a good incoming
rush of water disturbing its contents. I'd be tempted to lift the grid,
don long rubber gauntlets(!), and give the gully a darn good clean out
before investigating any further.

David