Flush with regular water at least once, make sure it warms up to where the thermostat is opened and burp the vehicle (put front wheels on ramps, and if possible, facing upwards on an incline if you have a sloping driveway), running full heat inside the vehicle. Drain system. If it looks really nasty when you drain it, repeat with regular water.
Refill with distilled water, heat burp and drain, then run that 50/50 asian mix you just purchased, top off and burp system. Should be incredibly clean if you do it this way.
System takes around 8.3 to 8.5 quarts.