The siphon or shower drain empties when flushing the toilet.

Ok. So I can't really do much about that myself. Then I have to contact the plumber. Would it be possible to fix it without tearing everything up?

There are also pipe ventilators or, better BE-ventilators, which can be attached directly to the pipe. However, I have never had one myself...

How big is the average pile clogging a pipe system? :)

Well, after a hard night, quite a lot can definitely add up... :p But seriously, as everyone here has already said. The problem is definitely with the ventilation. Regards, Olli

That would be shoddy work if something was not installed correctly. And it can't stay that way in terms of odor either.

That would be botching if something wasn't laid out correctly. And it can't stay like that odor-wise either.

something like that can happen... Of course, it can't stay like that, so get the GWS trade back in. Olli

The venting of the 100mm pipe upwards is really missing. (Venting of the wastewater pipe, not the room air!) The toilet flush empties the shower by negative pressure. Unfortunately, these flat construction methods greatly favor this. There is little water in the siphon and minimal negative pressure is sufficient.

Where is the next venting of the wastewater? You can only see where the pipe disappears downwards.