platic hose inside the tank the sucks fuel from the bottom of the tank. You can check if it fell off by unscrewing the fitting on the backside of the tank (behind airbox, by steering stem). When you unscrew it the hose should be on the back side, if its not youll have to fish it out of there and reattach it, or make a new one.
Also when you unscrew the fitting, note your fuel level in the tank first, so you dont have gas pouring out of it.