That should be the crankcase breather tube.
3.5mm
The PVC valve for a 2005 beetle is in a tee hose. The hose is on the front right under the intake manifold.
if one was put on the car it should be in-line. you should find it in the hose leading to the carb just before the hose goes in to the carb. if you don't see one there you should put one there.
At the to of the radiator.
You can install a circulating block heater in your 2001 VW Beetle on the bottom radiator hose. The installation is quite simple.
Check at the end of lower radiator hose.
There is a large black plastic hose that runs from the air cleaner box (behind battery) to the intake manifold behind the engine. It is on the firewall behind that hose.
If you have a manual transmission and a centrifugal advance distributor, you don't have any. If you have vacuum advance on your distributor, there's one vacuum hose running from the side of the carb to the distributor. If you have an automatic transmission, you've got a hose from the intake manifold to the control valve.
Follow top radiator hose to the engine & you will find it
To add water to the radiator on a new beetle, first remove the lower radiator hose. Then add water to the coolant reservoir.
More information please Make? Model? Year?
on a 3.1 v6 it is on engine at the end of the top hose before housing,the connecter is black on sensor. on engine beside hose!!