Since no pictures exist on the internet (that can be found) on where exactly the drain comes out at, hopefully this picture will help describe how you can help yourself figure this out:
I found this video of a guy removing the AC box from an e46 330i. In the above circled area is the drain location on the AC box itself. This would correlate to the center of the car, directly over the front half of the transmission. You will have to get under the car (make sure it is safely placed on jack stands) and look from the back of the car forward at the end of the transmission, between the transmission tunnel (floor of the car) and the top of the transmission. If you can squeeze yourself in there right, you should be able to see all the way forward enough to see where the drain comes down through the floor and to where it goes. It should be about the only thing which is in this position (remember: center forward portion of the transmission). Through looking at all of the other BMW photos, I can tell you that BMW has placed the drain on the left side, the right side, on both sides, and has just let it drain on top of the transmission. Your guess is as good as mine. What I can tell you is, it will be a soft rubber hose. Depending on the angles which it will bet to actually get to the AC box, it may not be easy to clear any blockage.