Interesting for all Passat owners from 1996 onwards. (Solution)

Recently, the car smelled extremely rotten.
Then it was gone again.
That sometimes happened again.
Now, I accidentally discovered that the drain in the water tank was completely blocked.
That means, the air that was sucked in was moist and foul-smelling.
The problem with that is... you can't see the process.
Only when the battery is removed can you access the drain.
The car is now exactly 4 years old. After such a period, this can always happen if you don't always keep the container clean.
Tip: In the drain opening, there is a thin rubber gasket that is simply inserted.
These are the ones I've removed.
This prevents any debris from accumulating on this relatively narrow and tight fitting.

Best regards, Alex