"Jose" wrote in message
m...
The aux tank was connected directly to the engine after the aircraft fuel
system, Not to the wing and the provided documentation and system
description mentioned nothing about the fuel return to the main tanks.

How would the fuel get to the main tanks in the first place? Is the
engine the only connection? (if so, with the fuel selector OFF that
should block fuel flow to the main tanks). Is there a vent line that
connects them?

Excess fuel from the engine is returned to the main tanks. Twin Cessna's
are the same way; if you switch to the aux tanks before burning a certain
amount out of the mains (90 minutes for the large aux tanks) the mains will
overfill and vent overboard before the aux tanks are empty.

Allen