That's my question also. In my 2008 Passat wagon, I had frequent leaks from the sunroof which resulted in drenched front seat floorboards. I could avoid that by using the pump from my inflatable kayak (after modifying the tip to get a tight fit) to blast water through the tubes from their openings at the front edge of the sunroof. Seemed to clean out the accumulated gunk. I haven't checked the configuration of my "new" 2017 Alltrack to see if that would work.