Building Regs. Do all WC cisterns have to overflow to

[PeterRayner]

Hi everyone. Can anyone tell me - do Building Regs require that a W.C. has to have an overflow pipe from the cistern to the exterior of the building?
My cistern is a slim line type to be boxed in.
Many thanks for any reply.

 

[Paul Barker]

modern designs overflow through the close coupled joint into the pan. Both drop valve and syphon designs. Because drop valves are on the whole very poorly sealed water passes constantly into the pan for a good 6 months on a newbuild estate, must make the water board a fortune. The migration from lever flush syphons to button flush drop valves was not on the basis of mechanical superiority but bling.