WARNING: This page is about a different car, the 2002 BMW M Roadster, 2002 BMW M Coupe, 2001 BMW M Roadster, and 2001 BMW M Coupe. However, it is still accessible from the selected car via links, so may be relevant.
Unfasten vent screw on expansion tank.
All bleeding occurs through vent plug on expansion tank.
Cooling system is vented after the filling procedure.