You can find the drain from inside the car, too. It's t he black rubber hose that attaches to the evaporator housing and the floor board. You need to clean it out with compressed air or suck out the muck with a shop vac.

If the evap drain isn't your problem, do you have a sun room? Have you ever cleaned the sun roof drains? It's the same situation as the evap drain except you have 4 to clean...