The Easi Plumb 1 Part Internal Overflow Siphon is suitable for use in low level and closed coupled WC cisterns. Pressing down on the lever lifts a plastic washer which raises the level of the water above the spill over point. At this point the water in the cistern will flow down through the tube by siphonic action into the toilet bowl until the siphon action is broken. The siphon can be set for two flush options by inserting the tab supplied into the either the top two hole (Full Flush) or bottom two holes (Half Flush). All siphons come complete with siphon backnut/washers and low level coupling nut/seal as standard.