This should help answer your question:

http://auto.howstuffworks.com/cooling-system7.htm

Now this reservoir bottle hose, are you hooking it up to the radiator cap? The radiator cap sends excess coolant to the bottle (when things get hot), and pulls it back in when it needs it back (when things are cooler)...

Did your car not come with a reservoir bottle hooked up to the radiator cap?