Developed by two engineers in Finland, siphonic roof drainage made its first appearance in Europe in 1968. Unlike traditional roof drainage systems, a siphonic system is designed to operate with the piping completely charged with water during a rainstorm. A siphonic roof drain has a special insert that acts as an air baffle and anti-vortex vane such that only water is drawn off of the roof, not air. Several of these drains tie into a horizontal collector that is routed to a convenient point where it transitions into a vertical "downpipe." This downpipe, once it reaches the ground, is piped to a vented manhole or inspection chamber where the water is discharged at atmospheric pressure into the storm sewer.