A tube, usually made of aluminum, positioned inside an underground storage tank fill pipe and extending to a point about 6 inches from the bottom of the tank.

The drop tube reduces turbulence when the tank is being filled.

Instead of splashing into the nearly empty tank from the top, product entering the tank is routed through the drop tube where it emerges near the bottom of the tank. This serves to minimize turbulence and, as a consequence, minimize the creation of vapors.