Sulphur smell after shower

[SussexBornAndFed]

We have a curious (and gross) issue in our house at the moment. We have a shower in an en-suite and every time we use it, there’s a really disgusting egg smell, but not from the shower or in the bathroom but downstairs in the kitchen and hallway. Sort of under, but not directly under the shower. And also not near the soil stack or drain?

We’ve put a drain unblocker down, we’ve run the shower, and if anything it’s getting worse.

It seems to be coming through the ceiling?

Any help, I’m at a total loss.

Was this shower added after the house was built?

I suspect a plumbing defect. Might be a leak between floor and ceiling, is very often a unvented soil pipe. Builders like to vent them with a "durgo" or similar, which they hide away behind boxing. Notionally it allows fresh air to enter the pipe when there is suction, and prevent smells escaping when there is pressure. They go wrong.

If you have long horizontal waste pipes, waste will not flow away easily.

Try to work out how the waste from this bathroom finds it's way to the house soil pipe, which would originally have been placed on the wall of the original bathroom.

You need to clean the pipes. I get this every so often (for me it is when I empty the bathroom sink - it must move the gunk settling in the shower pipe or something because it is definitely coming from the shower plug hole. I poured a load of bleach down there and it sorted it. Have to do this every 4-6 months or so.

Sorry didn’t read your full op!! Apologies. Ignore me and listen to piglet.

Ah, Pigletjohn, yes. Our house was built in the 20s and someone did an awful, awful reno about 15 years ago. Everything we go to fix has been bodged. This shower is in a long line of things that have gone wrong.

The waste from the shower goes out under the floor and then down in a boxed section and out of the house to the sewer. This boxed section has lots of bathrooms going into it. We have no idea what state the plumbing is in the boxed section but I suspect it's been done shoddily.

Perhaps we should uncover the box to see if there's a failed Durgo (we've had these before in a flat)

Thank you