A drop tube designed to allow the flow of both product and vapor through a single fill-pipe riser. The diameter of a standard drop tube is just slightly smaller than the inside diameter of the fill-pipe riser.

The diameter of a coaxial drop tube is about an inch smaller than the diameter of the fill-pipe riser. Small tabs on the outside of the coaxial drop tube keep the tube centered in the fill pipe, allowing vapors to flow upward between the drop tube and the fill pipe while product flows downward through the drop tube.

See also Drop tube and Poppeted coaxial drop tube.