Dikshaware A dual siphon-flush valve is a component used in modern toilet systems that offers two flushing options for conserving water. These valves are designed to provide a full flush for solid waste removal and a reduced flush for liquid waste, helping to reduce water consumption. The "6 inch" size you mentioned typically refers to the diameter of the flush valve, which is the opening at the bottom of the toilet tank where water flows into the toilet bowl during a flush. An 6-inch flush valve is a relatively standard size for many modern toilets