Abstract: A system for returning residual liquid remaining in a loading line to a liquid cargo container after loading or unloading of the cargo container. This system includes a liquid return line extending between the loading line and the cargo container. A pump is positioned to move liquid from the loading line, through the liquid return line, and into the cargo container. A vapor line communicates between a vapor space in the cargo container and the loading line. The system may include an optical liquid level sensor. The level sensor includes a light tube having two substantially straight sections joined by a substantially continuous curvature bend. The bend has a rounded cross-section and the light pipe is formed of a light conducting material. An optical emitter is positioned at the end of one of the straight sections of the pipe and an optical detector is positioned at the other straight section of the pipe. A micro-controller activates the optical emitter and monitors the optical sensor.