The Byelaw 30 kit  (England and Wales) comprises of a screened breather, screened warning pipe unit, ¾, 1.5, 2 ” dip tube bend, rubber grommet for vent/expansion pipe.
 
Byelaw Kits for Water Tanks
 
Byelaw 30 (also referred to as Water Fittings 1999) in England and Wales and Byelaw 60 in Scotland.
 
Any tank that is connected to a mains supply and is to be used for storing potable (drinking) water should have a Screened Overflow Kit to meet current water regulations. The tank should also be suitably insulated and also be WRAS Approved for the purpose.
 
The difference between the two codes is that the overflow dip tube must be 38mm (1.5 inch) in order to satisfy Byelaw 60 in Scotland, whereas 22mm (3/4 inch) is suitable for Byelaw 30 in England and Wales.