Thanks! Plumber came last night and sealed around the PVC tubing, if that doesn't work I will push for either him to do a smoke test or find someone who will.

Thanks, that sounds like a doable approach.

The plumber came yesterday night and sealed the rear of the toilet with bitumen/ asphalt - so far it seems to work, but it is also a little too early to tell since the sewer smell might be hidden behind the asphalt smell right now.

I asked about the vent pipe - he said that pipe is there to allow air to enter the pipes, not to leave the pipes. And since there are no issues with anything being sucked dry, it seems to work fine.

Will see if it the sealing already works, and if not, the smoke test sounds good.

But I like it :)

Yeah I looked again at my toilet here - it flushes to the rear (but stands on the floor - so not a proper hanging toilet either), and there are multiple PCV pipes / couplers that go into the wall. All quite crusty and old.

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Removing that toilet and redoing the PVC portion is more than I would endeavor, but I suppose that this is what the plumber had in mind.

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Any intermediary solutions, such as drowning it in Silicone?

Or will that not work on PVC anyway?

Weird, I could have sworn that I had responded here already. Anyway:

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Could you speak a bit more about the seal? If I assume that the underfloor siphon and ventilation work, then the portion of the pipe that could be affected by a leak in the seal would only contain a limited amount of smelly air, right?

This toilet is stepped on regularly, for example to turn off the gas outside. I also did install a new toilet seat, which doesn't involve drilling, but a fair bit of shaking and movement - could these things have unsettled a seal?

It's sewer smell, good thinking though!

The underfloor siphon actually is for the toilet (and I think the shower and sink also go through there). Meaning "it is located underfloor".

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So:

• Sink: Has a siphon directly underneath, then feeds into the underfloor one.
• Show: Assume the same.
• Toilet: Directly into the underfloor one.

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All of these look alright (have water in them, plumber also didn't see anything odd when opening the underfloor one).

How does this look to you? This image from outside show the bathroom, I assume the vertical pipe is my vent pipe and might be blocked somewhere?

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https://abload.de/img/complete_viewyudx5.jpg

Adding to the ventilation hypothesis. The following is a look downwards from the bathroom window.

Here is what I see:

• The pipe on the right is gas.
• Looking down, I see that all bathrooms have their individual ventilation, correct? So they would not have the same problem.
• The pipe on the left appears to emerge from my bathroom. Is that the ventilation pipe headed to the roof? I’ll go there now to check it out.

https://abload.de/img/87922e5a-5f57-4ac5-bqce47.jpeg

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Update

This is the exterior view of the bathroom (the left window). It looks to me as if the pipe on the right hand side of that window emerges from that bathroom, then moves up and ends in an inverted U.

The pipe on the left that also crosses horizontally is gas and can be ignored.

All bathrooms below seem to have their own ventilation.

So most likely that pipe deserves some checking?

Yes, fair question.

1. In that case, wouldn't the 5 floors below not also complain about the same? Or is that something that I would feel heavier on the top floor because the gases move upwards?

2. No way to check this myself I suppose? How would one go about this - a professional to check from the roof?