Stench from the sink or siphon - Where does it come from & how to eliminate it?

Good day,
There is a strong smell coming from my sink or siphon.
I have already tried letting vinegar and salt sit overnight, after which the smell was gone for 2 days.

Furthermore, I completely disassembled and cleaned the siphon.
That did not help either.

What is the cause?
What can I do about it?

Attached are 2 pictures

Is there always water in the siphon?

It may happen that the siphon is emptied when operating the toilet flush, for example if the vent pipe is undersized.

I am a tenant in the apartment. What course of action would you recommend to me now?

It is also possible that roommates are flushing all sorts of things down the pipes, which causes unpleasant odors. Do other tenants also have unpleasant smells?

Best regards, Sigi

It is also possible that roommates are throwing all sorts of things down the pipes, which results in unpleasant odors. Do other tenants also have unpleasant smells?


Regards Sigi

I don't know that