cruzer82,
Hope this helps:
The a/c drain condensate drain clogged on my 1999 C5 coupe, causing water to backup into the passenger footwell and enter the computer compartment. Water followed the computer wiring and entered it, ruining it and immobilizing the car. I was out-of-state on vacation, and the car was repaired under the new car warranty. It was out-of-service for five days.
You can reach the rubber drain elbow from underneath the right front of the car while the engine is cold. Use a jack stand if you raise the right front with a jack.
You can see the rubber elbow exit the firewall, behind the right engine head. You can use a small "tack puller" type screwdriver to help you remove the rubber elbow from the plastic nipple the protrudes from the firewall. There is not much space but you can remove the elbow if you are patient and the engine is cool.
Remove the elbow, clean it out, and cut off the nipple end. You will see that it is moulded into a small opening, which is prone to clogging and doesn't drain fast enough during high humidity.
I used a small amount of dielectric silicone grease on the inside of the rubber elbow (plastic nipple mounting end) to help me replace the elbow.
You MUST clean this drain or you will severely damage your computer and other components such as the HVAC blower motor when the water backs up.
Good luck - this is a common design flaw that Chevrolet has ignored on the C5.
