The minimum and maximum volume of water used at each flush. Where a single flush is used, the value of upper bound and lower bound should be equal. For a dual flush toilet, the lower bound should be used for the lesser flush rate and the upper bound for the greater flush rate. Where flush is achieved using mains pressure water through a flush valve, the value of upper and lower bound should be equal and should be the same as the flush rate property of the flush valve (see relevant valve property set). Alternatively, in this case, do not assert the flush rate property; refer to the flush rate of the flush valve.