With a recovery type cap you could literally have a hose running into a mason jar with no lid on it, and it would still work like it is supposed to........................Then when the system cools down and the coolant contracts .................... causes a vacuum and that little valve on the cap picture I posted has a very light spring holding it closed, so the vacuum can pull the coolant back into the radiator.
The three critical points are..............
.......... that the recovery hose needs to be submerged in the coolant to recover it
............ and that the recovery hose from the radiator to the recovery tank HAS to be air tight.
............AND the tank needs to be vented ................
