Water flows from the cistern in to the pan under gravity, carrying the waste out in to the drain. They are dependent on a sufficient volume of water to perform the task, but the flushing mechanisms used in standard WCs often result in leaks. Water regulations require all new WCs to have a full flush of no greater than 6 litres. Some standard WCs are available with a full flush volume of under 6 litres, but as water volume reduces, so does available performance. The reduction in water can lead to double flushing.
This uses the same flushing principle as standard WCs but the cistern is provided with a reduced flush of no more than two thirds of the full flush which is intended for liquids as opposed to the full flush intended for solids. Again, the reduction in water can lead to double flushing.
Instead of flushing with water flow and gravity, waste is shredded into slurry and electrically pumped through small-bore pipes to meet the drain. This can be noisy and prone to blocking the shredder.