Over the past 6 months I have been in a battle with water penetration into my '06 M45. From searching on this forum and others, it seems like a fairly common problem with different causes. Through various methods I eliminated all other possibilities of water leaks that I had come across: windshield, A/C condenser, sunroof seal, etc. All signs pointed to the drain tubes. Problem was that none of the fixes I tried worked. I tried blowing compressed air in them, I tried running hot water down the tubes, I tried running different kinds of wires down the tubes, etc. I was convinced that my problem was a clog at the end of the drain tubes. Turns out I was right but the reason it took so long to figure it out is that there is no real specific guide or pictures or video online or anything in the service manual regarding drain tubes. I always assumed that the tubes ran from the sunroof, down the A-pillar, and into the engine compartment to the bottom of the car where they are not accessible. Well that is not accurate. The tubes terminate outside the cabin at the front of the dash at the bottom of the windshield. The tubes drain into the same place that water drains from the cowl outside of the car at the base of the windshield. However, I only found this out after my friend suggested just pulling hard on the tubes to see what happens. He correctly reasoned that I was in store for a trip to the dealer whether I ruined the tubes or whether they remained clogged.
So I would love to say that after all my semi-scientific approaches to narrowing down my problem to the drain tubes that I also scientifically discovered where they terminate. But the truth is I just pulled like hell on one and it popped out. So I did the same on the other and it popped out as well. Look at the below pictures to see what we are dealing with in these cars. You'll notice that on the end of the tube there is a black rubber grommet. The tube is somehow very solidly connected to the grommet which is why pulling on the tube turned out to be no problem...again just pure luck. But take notice of the end of the black rubber grommet. You'll notice a little rubber flap that I have to assume is meant to prevent dirt and debris going back up the tube. What this little flap actually does is trap dirt that gets in at the sunroof and runs down the tube (you would be amazed at the amount of water and dirt that gets past the sunroof seal). So my fix was simply to remove the little flap. After 3-4 really strong spring thunderstorms here, I can safely say it's been bone dry in the car.