Every water closet pan shall be supplied with water from a flushing cistern, pressure flushing cistern or pressure flushing valve, and shall be so made and installed that after normal use its contents can be cleared effectively by a single flush of water, or where the installation is designed to receive flushes of different volumes, by the largest of those flushes.
No pressure flushing valve shall be installed -
in a house, or
in any building not being a house where a minimum flow rate of 1.2 litres per second cannot be achieved at the appliance.
No flushing device installed for use with a WC pan shall give a single flush exceeding 6 litres.