You can search for the diagram on http://getbmwparts.com/
I haven't drained the radiator before on my car so someone else will need to chime in here.
When I have done radiators in the past, I've always cut the hose and drained it. It makes it easier to remove the hose when it's cut in half.
2010 E63 Black sapphire metallic
“Speed has never killed anyone. Suddenly becoming stationary, that's what gets you.”