My original question was, does it matter whether the pipes are charged and full or not? I can't see why it would matter. I do appreciate the other comments.
No it won't matter. About the only way you would have an issue after draining is if some water was trapped in a fixture and not allowed to mix with the antifreeze.
BTW, you don't need 12 gallons unless you have a ten gallon water heater and you don't need to pour additional pink in the traps. When you run the pink out of the fixtures, it will displace any water in the traps.
FWIW, I've done winterization close to the way you've done it---drain system and pump antifreeze through everything, including the water heater. Next Spring, you can drain the antifreeze, including the heater, and flush with water. I don't get any residual taste or odor.
Good luck with your rig.
