A/C drain plugged!

I've got a '92 Lumina 3.1L. I'm pretty sure the drain for the evap core is plugged. A/C runs great for a little bit, then i start to get water on my floor. It's not anti-freeze, so no worries there. I was wondering how to access the drain so that i can unclog whatever is blocking it. I'm not sure where it runs out the underside of the car or if it can even be accessed from outside. Any help is greatly appreciated.

I finally had some time today, so I broke out the tools and decided to give it the 'ol college try. Good thing about GM's is that most things can be undone with a 7mm nut driver. :) I went to autozone.com got a semi-helpful repair diagram for the heater core. It sure doesn't have every step in it. For anyone doing this in the future, there's about 8 or 9 screws holding up the lower case with a few in hard to reach places!

Finally got it down and it looked fine. Seen the little rubber hose that the drain pan connects to and decided to pull it out. Took a good look inside and there was a dustbunny the size of Texas in there! OK, well not that big, but big enough to block the 1/4 in. hole. Removed troublesome dustbunny and reassembled. PITA to get the drain back in to the firewall because it's "L" shaped. But got it after about 10 min of persuasion.

It's nice to be able to use the A/C again, even though summer is almost over.