51¶¯Âþ

When the valve on a WC cistern wears out, it no longer cuts off the water
supply when the cistern is full. The result is usually a stream of water gushing
out into the street. Now B. McManus of Yorkshire has patented a way of
preventing this (GB 2 334 043). The design has a secondary float chamber which
is normally dry. When the main cistern overflows, a float in the second chamber
rises, locking the flushing lever. This tells the householder it’s time to call
a plumber.