Actually(!) it shouldn't smell if there is water standing in the siphon. The siphon can actually(?) only run dry if either very very little water comes from your side (it simply dries out then). We can probably rule that out, since you do wash dishes and so on. Or if on the wastewater side, occasionally or constantly, a vacuum develops that sucks the water out of your siphon.
Ideas:
- Let hot water run, then check by touching if your siphon contains water.
- Let hot(?) water run regularly and observe the smell (for example, be at home on Sunday and let water run every hour for 1 minute so that the siphon is filled).
- Try to figure out by careful watching and listening whether the siphon is being sucked empty.
Questions:
- Are there any leaks in the wastewater pipe after the siphon? The photo suggests an adventurous construction, is everything tight there? Any slip fitting with play?
- What kind of angle valve is that there?
Alternative procedure:
- Report the defect to the landlord ("smell"), request remediation, set a deadline, and if the defect persists after the deadline, reduce the rent appropriately. (Don’t waste the money, who knows...).