[KULTULZ]

A guy here in town told me that the cap had to be one that has a vacuum valve or something like that so that the coolant could be sucked back up to the radiator to refiil the radiator.

No special cap needed although one was offered.

What happens with a recovery bottle is that when the coolant cools after shutdown, it creates a partial vacuum causing the radiator cap to open (valve inside) allowing outside air to be drawn equalizing system pressure. Once equalized the valve closes.

With the bottle, the system draws coolant rather that atmosphere and that prevents air bubbles/air locks in the system. It also allows coolant that is purged due to heat expansion to be sent to the bottle rather than the ground.