To fully drain the system requires removing the block drain plugs in addition to the radiator drain, and usually blowing some air through the heater core. With those tricks I can get about 9.0 quarts (give or take) into my system which is rated at something like 10.0 or 10.5? The fill spec is for a completely empty system and you'll never put that much in.
I flush & drain as much as I can, add 1 gallon of Mercedes a/f, a bottle of Water Wetter, and top up the rest with distilled water. In warm climates where it rarely gets below freezing you can cut that down to two quarts a/f, as long as you don't plan any trips into freezing weather! That helps the WW keep the engine a bit cooler where summers are blistering (Sacremento, Phoenix, Tempe, Death Valley, etc...)
