P68 fuel systems
It is a good idea to study the fuel system in p68's as it does have a couple of tricks.
The fuel selectors have sometimes been known to seize up so they cannot be moved. It is worth checking these regularly. But I was always wary if making changes to fuel selectors immediately before takeoff.
One operator I knew took his family for a trip in his P68 and when he got to his destination he selected the fuel selectors to "crossfeed-engine off" . He then had the aircraft refuelled to full tanks and went off for the night, thinking he had turned the fuel off.
But the aircraft was parked on sloping ground and when he came out in the morning he found it almost balancing on one mainwheel, with fuel dribbling out of the fuel tank vent on the downhill side, and not much fuel in the uphill tanks.
Most embarassing, and he also had to pay a hefty call out fee for the refueller.