The syphon is a leak free component – providing the back-nut is tightened sufficiently the cistern cannot leak.
The cistern does not have to be fitted to an external wall for an external overflow, so it is perfect for closet toilets or WC’s which are in the middle of a building.
The overflowing water will alert the user immediately if there is a problem as the water flow can be seen running into the pan, and will cope with at least 30 l/min