During normal operation, liquid sulfur flows into the seal leg via a rundown. Once inside the device, sulfur flows downward through the inlet piping to the bottom of the leg, and then upward through the annular outlet piping to the sulfur outlet. Similar to a P-trap, liquid sulfur in the bottom of the seal leg establishes a vapor seal, preventing H2S and SO2 vapor from passing into the sulfur pit or collection vessel.