This particular 414 came standard with two tanks per wing, tip tank and an aux tank in the wing. To this could be added a locker tank. The later 414A had just an integral tank in each wing, simplifying management. The diagram is for a 310, which is a similar system to the 414. Had sufficient tip fuel not been burnt initially it was possible, if you switched to the aux, to lose fuel via the tip vent as the tank overfilled with engine return fuel, or when transferring to the tip from the locker tank. You wanted to transfer the locker tank early in the flight to ensure that the pumps worked and did transfer, bearing in mind the previous necessity to have room for it in the tip.
