This is a good way to illustrate it.
If this were from the roof view….
The box is the vent and the tube goes up into it.
But the tube below the roof is attached to the ceiling panel.
The tube does not connect to the box in any way, just sort of hovers there inside it.
The vent – doing what vents do – they vent, is full of holes.
Water just pours in these vent holes and down in between the roof and the ceiling panel.
Where the insulation is.
Again JEEN EE US