Pumping fuel backwards through an electric fuel pump

Thanks for the suggestions so far. I had already considered both of
them:

1. Filling on the ground, and gravity draining in flight

For optimum "go fast" trimming, I really need to be able to transfer
fuel rearwards in flight, once at altitude. The plane will fly
fastest and most efficient when trimmed so far back that it's unsafe
for take-off ... or anything but fairly straight-and-level at high
altitudes. I'll want to pump some forward again as I'm decending to
land. (And no, I'm not crazy enough to go WAY back out of the
envelope.)

2. Filling with water instead of fuel

Ya, that's certainly the safer thing to do, and is in fact what one
builder is planning. I'd still have the transfer-in-flight
consideration above, of course. And I'd really like to be able to
have those extra 12 gallons onboard (when rear seats empty) for extra
range. I just hate carrying around dead weight. I'm also planning on
routing another line from the aux tank to the engine, via a shut-off,
so that it could gravity-feed directly as a fail-safe. Tougher to do
with water. ;-) This fuel cell is from the NASCAR circuit and it very
well built, and way back in the tailcone; I'm not terribly worried
about it in a crash.

Meanwhile, I've found a site (misplaced its link at the moment, but
can find it again via Google) that sells Facet pumps with integral
valves specifically intended for fuel transfer. When OFF, no fuel can
flow in either direction. The idea is to use two of them on separate
"fill" and "drain" lines of course, with no extra manual valves
required. They're cheap enough, and eliminate other hardware, so I'll
probably go with them ... even tho' they'll require the second line
plumbing. Unfortunately, they're only 30GPH, and I'd like to find
some with at least twice that capacity. I'm still looking.

Greg