[Wayne 962]

Short of pressure washing / flusing the entire system, it's nearly impossible to get all the old fluid out. The *only* way I know of to do this is to take the entire system, empty it, then fill it up again, run the car for a short while, and empty it again. This will get almost all of the old fluid out, but is pretty costly when you use the Genuine BMW coolant.

In reality, it probably won't matter too much if there is other coolant in there. Just to be on the safe side, I would indeed do what you suggested - empty the system, fill it up with distilled water, let it run until it gets hot (with the heater on full blast), then empty it out again, nd refill with the BMW coolant. That is the procedure I'm currently doing on my 5-Series...

-Wayne