[1795]

That helps clarify things a little better, in the first post it sounded like you were going to run the expansion tank dry. Your expansion tank sits lower than mine, mine is the upper most piece of the cooling system and sits on top of the transverse leaf springs tower. If you plumb the hose to the catch can into the bottom of the can it could get sucked back into the Harrison tank, if you plumb the hose into the top of the catch can it will not suck anything back into the Harrison tank unless the catch can gets filled to the level of the hose entering it.