the jugs you can drain fluid from the 10mm bolts on the sides, removing the water pump cover is the lowest point, that should remove most coolant.
maybe get a aftermarket water pump cover with a drain and a billet high flow impeller if you dont already have one.
to flush it, id drop the coolant, refill with water, run the engine then drop the water maybe do that twice to make sure there is no coolant in there..
then run that prep fluid through there and drop it as instructions say, that should dry up most of the water. and then run that expensive shit.
i wouldnt bother with it, do the main cooling things, bigger rad, billet ultra flow impeller, cool head some decent coolant, get it tuned well and you should be fine, just dont keep revving the shit out of it in a stationary position.
that waterless coolant actually run a bit hotter, but doesnt over heat.