Cessna 177 Owner's Manual page 22

Take off with the fuel selector valve handle in the BOTH ON position
to prevent inadvertent take-off on an empty tank. However, during
long range flight with the selector valve handle in the BOTH ON
position, unequal fuel flow from each tank may occur if the wings
are not maintained exactly level. Resulting wing heaviness can be
alleviated gradually by turning the selector valve handle to the fuel
tank in the "heavy wing". The recommended cruise fuel management
procedure for extended flight is to use the left and right tank alternately.
With low fuel (1/16th tank or less) a prolonged powered steep descent
(1,000' or more) should be avoided with more than 10° flaps to prevent
the possibility of fuel starvation resulting from uncovering the fuel tank
outlets. If starvation should occur, leveling the nose and turning on the
auxiliary fuel pump should restore engine power within 30 seconds.
FUEL SYSTEM QUICK-DRAIN VALVES
NOTE
NOTE