Larry Dighera schrieb:

What would prevent plumbing the fuel return line into the top of all
fuel tanks above the fuel level, so that the returning fuel would be
able to fill whatever tank space was available at the time?

This would prevent an informed tank management.

It is much easier just to tell the pilot to burn 90
minutes out of the mains before switching to the aux's.

It would seem a placard would be more prudent.

If this simple instruction is already too complicated for a pilot...

Stefan