A "recovery" system will have the hose enter at the bottom of the tank (at least usually). That way it (the radiator/engine) can suck coolant back out.
You then use a recovery rad cap that has the little dime size metal 'button' on the seal side (the part below the big spring). That little button will allow the flow back into the rad under really light vacuum conditions (when the coolant is starting to cool and contract).
Very effective--you want it.