I have reconnected my Pside front tube. There is an access hole in the rubber matting which allows you to fish the two ends out and reconnect them. It isn't easy but it saves removing everything in the dash to get to it. Removing the dash is not desirable because the steering column must be lowered and probably even removed. For the Dside front tube, there is no access hole. Should yours become disconnected, I recommend locating the access hole for the Pside, and then cutting a small square flap into the rubber matting on the Dside at the same position. Shame on GM for making the tubes in two pieces.
The ends of the tubes terminate in the front wheel wells in a nipple. This nipple is a nice design in that it prevents gunk from getting splashed up in the tube, but the nipple is just too tight. I recommend that as part of yearly maintenance, you treat the nipple with silicon to keep it flexible. When it dries out it gets stiff and seals itself shut. In fact, if your tubes become clogged, I recommend first pulling the fender liners, and giving the nipple a squeeze - water will probably come out. Should you need to clear the line further, try threading some flexible wire up from the bottom or down from the top, before pulling the headliner.
As for the rear tubes I recommend pushing the tube through the body grommet to clear the nipple so the water can drain straight out. Tropical storm Fay come through here and so far my sunroof hasn't backed up with water - tubes are flowing sufficiently. I apologize for not having pictures - I had to get the car back together in a hurry.