Cleaning out the drains is simple BMW maintenance, is not only very easy — is necessary. If you neglect this simple task fallen leafs and road grime will clog the drains. Once your drains clog water can flood the cowl and come into the cabin through the fresh air vent.
Since Robot HQ is in the tropics, and monsoon season is now in full swing, we are keenly aware of clog drains. You would also if you’d ever have pump out 5 gallons of water out of the back seat foot well.
So get yourself a vacuum get all the crud out of the drains, flush with water, and make sure that you can see the water coming out right behind the wheels about 2 inches after the corner of the fender. Don’t forget to inspect the sunroof drains (if your car has one). You and your headliner will be very happy you did.