Fitting a 40mm pipe to a 63mm downpipe. All aspects of plumbing questions and answers, help, tips and information

[Rich R]

Is there such a thing as a connector which enables you to fit a 40mm waste water pipe into a 63mm rainwater downpipe? Local plumbers merchants insist no manufacturer makes one. I find that hard to believe!

[Fixter]

The prob with this is that s lot of nasties can be shoved down a kitchen sink, causing it's water to be classed as 'black water'. Whereas handbasin, shower and washing machine waste is classed as 'grey'. Regs do not permit the mixing of black water and grey water in the same outlet pipe for reasons of heath.

[Rich R]

And yet it all goes directly to the same drain. Oh well.

[plumbbob]

It is not a question of what you are connecting in to or where it goes that dictates how connections can be made, but flow rates and diameters.

Storms may cause backflow along any direct connection to RWP and indeed the opposite can happen too with water seals being syphoned out of internal traps all because of the relative narrow bore of RWP.

You can connect to RWP but only by fitting a hopper and placing the 40mm outlet into it.

If the 40mm outlet is at ground level it should go directly to the drain as regulation dictates.