Draining coolant

Well my new water pump and gaskets have arrived so going to make a start replacing old one.
When draining coolant, do I have to drain from both the radiator and the crank case or can I just drain from crank case?
Reason I ask is the drain plug on the radiator was a bitch to get to and loosen last time and is only plastic therefore fragile. If I can get all the old coolant out from the crank case drain bolt, it will save time and grief.

Thanks all