Recently, Roy Smith posted:

"Neil Gould" wrote:
At most all you've learned is what the fuel capacity of your tanks
are, and that could be more accurately established while on the
ground, FWIW. In fact, the POH should suffice, unless you intend to
violate FARs as a regular practice.

What FAR says you may not run a tank dry?

The FARs address minimum fuel levels when you arrive at your destination.
If you have less than the required amount when you land, you are in
violation. If you are managing your fuel consumption adequately, there is
no need to run your tank dry.

Given that "how much fuel you really have in your tanks"
is only one factor in how long you can continue to fly, and that
those other factors aren't addressed by running your tanks dry, what
*is* the point in doing so?

Assume you are flying something with two tanks and no "both" position
on the fuel selector. You're 30 minutes from your destination, which
would you rather have: an estimated 30 minutes of fuel left in each
tank, or have one tank dry and an estimated hour's worth in the other?

I regularly fly something with two tanks and no "both" position (PA28),
and my preference is to arrive at my destination with more than 30 minutes
worth of fuel, period. I see no point in pushing those limits any more
than seeing how much over gross I can fly. IMO, such points are just
useless information. YMMV.

Neil