After replacing a section of coolant hose, I flushed my coolant system and filled it up with a 50/50 mix of coolant and water. But then I couldn't get any flow in the system; only one line was heating up.

After trying all sorts of ineffective ways to get the coolant moving I re-flushed the system, but this time afterwards I didn't add any coolant, just 100% water. I then figured out the flow problem--now everything is getting hot and works perfectly.

But my question is: how do I go about adding coolant now (in the proper 50/50 ratio) so that I don't introduce more air into the system while doing so? (trapped air bubbles were what I think was causing the initial problem)

Can I just open the lower radiator drain (to let some water out) and simultaneously add undiluted coolant to the expansion tank? Will this cause air to get trapped again anywhere? How much coolant do I add to get my system around 50/50 again?

Thanks for any help on this one. I know it's probably a no brainer for some of you, but I'm not familiar with the coolant system and all it's complexities.