12 quarts! You'll have plenty for future coolant drains.
If the coolant is well maintained, draining from the radiator is sufficient IMO. It doesn't get it all so if you are OC and want it all out, then you have to do the other drain *****, just adds more time to the drill. I had mine drained from the radiator, new thermostat swapped in, filled then burped in about 45 minutes.
If the radiator drain **** has not been removed for a long interval or the O-ring is heat cycled that little nylon part may leak or break. You may want to have a spare on hand. ~$15 I recollect.
I did the drill one time and the O-ring was dried out so it leaked from there following. No matter how fast you think you are getting the plug back in, it makes a mess.
Wear latex or nitrile gloves if coming into contact with coolant. Just a safety precaution in the event your have sensitive skin and or cuts on your hands.