Roof drain tube questions.

[AlanS]

2006 xc70. I discovered water in the well under the rear driver's seat...where the plate and wiring are. Not on the floor....I am almost positive it is coming from the tube that runs from the roof, down the pillar to a rubber outlet in the sidewall. Where does it begin? I blew through the tube (it separates at the junction of the exit tube)....nice flow. I think that it may be clogged from the sidewall to the outside. BUT...Still want to know where it originates and exits. Anyone else have similar problem?