Assuming there is no need to do a real citric acid type flush, this is what I do, for a routine radiator coolant swap, FBOW:
1) allow engine to cool
2) drain coolant, remove petcock if possible
3) clean and lube petcock o ring, close system
4) fill with tap water
5) drain and collect; this should still have some glycol
6) (optional) add radiator cleaning product and tap water, allow to sit an hour to overnight. Do not run vehicle. Collect if you do this step.
7) fill with hose, drain to ground
8) fill with 50/50 distilled with coolant
Done
Yes i realize this only gets 50% or so, but with longlife coolants and aluminum engines, the coolant and the system appears to stay pristine.