Greg,
If you're not planning to put fuel into the aux. tank during flight, and
only possibly drain it from the aux. tank to a main, then why not put a
simple hard line with shutoff between the aux. and main, and a filler
opening on the turtledeck? Put fuel in the aux. by shutting off the
transfer line and filling via the filler. Empty aux. to the main by
opening the transfer shutoff valve. No pumps, no checkvalves.

Russell Kent