1) Draining valve 2) Faucet 3) Regulator 4) Small faucet 1) Spigot 
A petcock (Pressure Equalisation Tap) is a small valve used to control the flow of liquid or gas. == Use on motorcycles == Most older motorcycles have a fuel petcock valve mounted on or nearby the fuel tank to control the supply of gasoline. In the United Kingdom it is known as a petrol tap. Meriden Triumph Bonnevilles have two petrol taps, one on...
valve for draining condensed steam from engine cylinders
The fuel valve, usually found on the side of the gas tank.
[n] - regulator consisting of a small cock or faucet or valve for letting out air or releasing compression or draining
noun regulator consisting of a small cock or faucet or valve for letting out air or releasing compression or draining
A petcock is a manually operated device inserted in the gas line that allows for an On, Off, and Res