yup, drain tubes. there are four of them. two forward and two rear. The front exut just behind the front wheel mud flaps in the "B" pillar. The Rear come out the "D" pillar. You will see little tubes poking out of the body.
I had to go from the bottom to clean them out. Since your sunroof opens you may be able to do it from above. I used shifter cable from a bicycle and fed it up from the exit. Poked around a bit, got some drips, continued to poke until it gushed out. Being in Washington, there was no shortage of water hanging out in there to help flush things out. Typically on my other cars I would pour water directly into the drain to help flush it. They were quite a bit more accessible than on the van. If I am not mistaken some people have used compressed air to clear them as well, but you have to be careful not to do it so hard that it seperates the tube from the sunroof assembly.