Overflow bottle question

Slappy, you kind of answered your own question. You have a overflow bottle and not a recirculating tank. You should be able to change the fitting in the bottom of the tank to run a line back up to the radiator and add a fitting on top for the vent line. Or just buy a cheap plastic one like I did.

http://www.jegs.com/p/JAZ/751518/10002/-1