The Dual Flush Toilet
Dual Flush Toilet Cistern
There are several recent cistern designs on the market which enable the toilet to be flushed using two buttons on the lid. I found these types leaked water into the bowl after flushing, due to the buttons being slightly depressed. I ended up having to put a spacer between the lid and the cistern because all of the adjustment to the buttons was used up. So the most reliable, in my opinion is still the old tested and tried siphon cistern type.
The cistern contents are basically the same, the water tank, ball-cock, and siphon with plunger plate and chamber. However, there are two distinct differences in the design, the lever operating the plunger is oval and operates up and down and, the plunger chamber itself has an air hole drilled at the half flush water-level.
This air hole is covered by the plate skirt by holding the lever down and operating a full flush allowing the whole contents of the tank to flow to the bowl. But, with a single-push and let go of the flushing lever, the water flows into the siphon from the chamber until the air hole is uncovered. Air is thus allowed to enter into the chamber and holds the rubber gasket against the plunger slots, breaking the siphon seal and stopping the water flow at the half-flow water level.
The Dual Flush Toilet Bowl.
The bowl is a very different design. Gone is the siphon effect which drew the water and waste away from the bottom of the bowl. The dual flush toilet bowl is designed with a larger outlet to the S bend, sometimes twice the diameter of the old bowl siphon type.
This allows the water and waste to be pushed out of the bowl by the flushing water, thus using less water. Some manufacturers claim that this type of bowl prevents blockages which were caused by the old bowl small diameter siphon design.
It is possible to retrofit the dual flush toilet cistern, but this has led to difficulties in flushing, sometimes requiring two or three flushes, mainly due to the original bowl being retained with the siphon still in place, obviously defeating the purpose.
A dual flush toilet can use as little as 3 liters in a half flush and 6 liters in a full flush compared with a conventional toilet which can use up to 20 liters a flush.