How Do I Remove An Air Lock From Hot Water Tank?

If the tank is for the heating system the air is bleed from the top of the radiators with a small key or long nose pliers.
If its for hot water open the hot tap and if nothing comes out put your mouth over the tape and blow hard the back pressure should move the air lock. Most tanks are self bleeding and the is not normally a bleed valve on them only a pressure releave valve which you shouldn't mess with,

I don't recommend sucking the pipe like a syphon but it can work in some cases

How come I keep getting air build up in my hot water heater even after it comes out the tap?  If I leave the water for a hour or 2 and go back to the tap there will be air come out of it again before the hot water starts.