Coolant expansion tank for e70 4.8

[neliconcept]

Hey guys,

So I just picked up a new expansion tank. I have done some research on replacing the tank and that seems easy enough. Lately I have driven it a couple of times and had to use the crappy prestone green coolant to not leak too much coolant. I do have two one gallon containers of the bmw blue coolant but will that be enough if I have to drain the coolant and flush it out? Also is their a radiator drain plug or do I just need to pull the lowest hose and drain that way? I haven't found much in the way of being able to flush the coolant on this engine, seen one for the n55 but that doesn't help me as it's setup quite differently.

Any help is appreciated!

Blake