All the more reason I use a flushing tee. After a power backflush with a garden hose I leave the cap off the tee and pour a gallon of antifreeze in through the reservoir tank. Air and water escape out the tee. I put the cap back on when I see antifreeze start to flow out the tee.
There still might be a little air in the system but a heck of a lot less than if I didn't bleed it off through the tee.
