Here's a presentation for do-it-yourselfers on how to change the Gen II Prius Engine Coolant. Most important thing I learned was patience when draining and refilling and bleeding out any trapped air.
As someone who spent the last several days patiently trying to work through an air-lock after changing the coolant control valve and inverter coolant pump, I recommend adding a "Lisles funnel" (~$26 on Amazon) to this procedure for the DIY'er. This will greatly speed up the process, prevent a lot of spillage, and doesn't require shop-air.