B Feelgood

I'll be installing a larger heat exchanger in the next few days and would like to drain and replace the coolant in the system at the same time. I know that there's an accessible drain plug on the radiator itself and a not so accessible drain plug on the engine block. How much fluid will drain from the drain plug on the radiator? Has anyone successfully drained the remaining coolant from the engine block as well? I believe the system holds 13-14 liters if I'm not mistaken.

Also, what does the bleeding process to remove air from the system entail? Any tips or tricks to be sure all air is removed?