Dual flush/water saving toilets can waste more water than they are ment to save. Dual Flush valves can run constantly if debris gets stuck in valve.
https://inhabitat.com/some-dual-flush-toilets-are-actually-wasting-water/
Also keep in mind water saving toilets in general have a larger opening between the tank and bowl as to let more water out at once to move the debris with a surge of water rather than a tank/flush using higher amounts of water.
https://inhabitat.com/some-dual-flush-toilets-are-actually-wasting-water/
Also keep in mind water saving toilets in general have a larger opening between the tank and bowl as to let more water out at once to move the debris with a surge of water rather than a tank/flush using higher amounts of water.