Depends what type of vents.....
Mostly they are vents that have a cover over them....they don't cause too much trouble...................
However the vents that are open.............

When you wash the frame first time they will drip out usually from either end of the vent.
The best bet is to avoid them. But iff you do do them you'll have to go back when the windows are dry and re wash just the glas underneath the vents to wash of the drip marks

:

David