My Lancair-235/320 has a float switch in the header tank which provides the ground for the control circuit of a relay that activates a pair of Facet pumps which transfers fuel from the wing tanks.  If the circuit is energized, the pumps come on when the level in the header reaches around 10.5 gallons and then turns off when the level comes up to about 11.5 gallons and cycles between those two levels.  Whenever the demand calls for an activation of the system, a light illuminates adjacent to the switch labeled AUTO FUEL.  When the wing tanks are dry, the light remains illuminated and there is a loud audible "rattling" of the transfer pumps which prompts me to turn off the system.

 

Most of the time I use the above described automatic fuel transfer system, but I have the capability of opening an interconnect valve which allows for transferring all the wing fuel to the header by either transfer pump via separate pump switches, or I can feed the engine directly from the wings via a fuel selector valve and opening the interconnect valve.

 

All 54-gallons (except for about a pint of fuel per side below the wing finger strainers) are usable.  12-gallons in the header and 21/21 in the wings.