Question id 110 - Aircraft General Knowledge - Airframe, Systems, Powerplant - ATPL - Airline Transport Pilot license

Can be used to drain the tanks, for daily checks.
It prevents a surge in the tank of an iced aeroplane.
Prevents low pressure or overpressure in the tank.
Prevents vapour lock in the fuel lines.

Training tests and timed exam simulations ATPL - Airline Transport Pilot license