As I type this my car is slowly filling up with water, I've tested and replaced my front sunroof drains but by rear drains clogged or leaking water into my interior. Is there any instructions on replacing the rear sunroof drains?
My .02 - When I had a bunch of water in my backseat, pulling up the rear footwell carpet on either side gives you access to the drains without issue to clean them out. - Most you'd need to do is (pull the front seats out, maybe) and fold up the carpet there to get access to the drains themselves.
Obviously if that doesn't work, then your drain clog is up at the sunroof and you're going to have to undo one of the oh **** handles and reach in above the headliner, pull off the hose and poke something in there to clean them out. Again not hard.