[gnorbury]

To give yourself a reference point of where to start looking, run the pump with the faucett open and check for air being draw up the pump inlet hose. This would indicate some sort of hole in the pickup hose, a bad connector or an empty tank (duh!).

I think its probably quite unlikely air could enter the system after the pump because the water is then under pressure and therefore leak out through the hole.

The only other option I can think of, would be a leaky pump valve. In this case you''d see air on the outlet side of the pump hose, but not on the inlet.

Good luck
Graham