Heater core

The way I do it is just connect the hose to the engine coming out by the Tstat, but LEAVE it off at the core, and prop it up so it's "up high." This provides an air path.

Then just fill it up. You can "dip" the hose down carefully into a can to get coolant, then connect. Fire it up and check the heater hoses. Both hoses should get warm. If not......no circulation.