I'm not sure I have the best way, or any way different than what other guys are doing. Most of my systems are closed loop, I always use Webstone isolation flange sets with the drains for this very reason.
Start by flushing and filling the system to rid of air.
I simply calculate the amount needed, have a sump pump in a five gallon bucket and an empty five gallon bucket for the drain water. Pour the glycol into the pump bucket, pump in while return water is captured in the empty bucket. I always figure for about 10% more glycol; as the glycol level lowers in the pump bucket you will have to switch the drain water hose to the pump bucket and some mixing will occur. Top off pressure with hose and nearby water supply.
This may not be the most expedient, or common way but it works and the tools needed are low cost.
"If you don't like change, your going to like irrelevance even less"
This post was edited by an admin on October 8, 2009 3:14 PM.