What is IO (internal overflow) and how does it work?
Overflow pipes were traditionally positioned so that any water leaking from a cistern could escape by dripping onto the floor or outside the building. This was a requirement under UK Water Byelaws to prevent waste of water: the principle was that a dripping overflow pipe was more likely to be noticed and the problem rectified. Internal Overflow is a system that allows any overflowing water from the cistern to be discharged into the toilet bowl. It is now allowed under Water Regulations January 2001.
