[Zderf]

Catch cans are usually just that... they catch the overflow for the system when it gets hotter than its normal operating range. Then as the system cools it creates a vacuum that pulls the coolant back into the pressurized portion of the system.

Good catch cans (not the plastic ones) usually have a port on the bottom to which your port "A" should attach and often includes some sort of drain valve as well. They are vented at the top (so they are not pressurized) which vents air as the can is filled with coolant. Air then is drawn back through this vent when the system sucks the coolant back out and through port "A".

You really should not need another "reservoir" of coolant available to your pressurized system unless you've got an overheating problem that causes the "catch can" to discharge overboard thus loosing coolant volume. That problem should be solved with water pumps, radiators, and coolant mixtures.

Just an idea or two. Anyway... it worked for me.

Zderf