A system for allowing an operator to accurately observe the liquid level in a tank truck or transport trailer that is filled from a bulk storage tank through a flange on the line from the storage tank that is attached to a matching flange of the tank truck or transport trailer by incorporating a float gauge structure into the flange on the line from the storage tank, thus, enabling the operator to accurately observe the level of the liquid in the tank truck or transport trailer and manually shut off the flow from the storage vessel when the tank truck or transport trailer contains the desired amount of liquid. The system includes sensors designed to indicate sealed engagement of the flange on the line from the storage tanks with the matching flange on the tank truck or transport trailer.