is easy....the hook up that I use is;
OUT of Header tank is "T"d and goes to the carb, and is how we're fueled.
VENT of Header tank goes to OUT of Main tank...
VENT of MAIN tank is vented to atmosphere.

How much fuel you get out is controlled by the clunks' fit in the tank....but this morning, when I did a test of this, it was very obvious that the header tank drew all the fuel out of the main tank, then it started emptying.

The amount left in both tanks was negligible.