40mm to 68mm Pipe Connection?

10 Jan 2017
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United Kingdom
Appreciate I've posted a few topics recently, but the help I've had while I've been working on my extension has been really very helpful. This time I'm trying to get my head around the best way to connect the rainwater downpipe and the washing machine waste pipe together (68mm and 40mm respectively). We are allowed to do this as we live with a combined system.

I've got tomorrow off work to sort the guttering for the roof. It's a simple pitched roof which extends the width of my house (5.5m) and outwards by 3m. The guttering downpipe (68mm) is going to run down at the side of the extension and at about two thirds of the way down, turn right on a slope towards the drain. Somewhere along and above that slope the washing machine waste pipe (40mm) will emerge from the wall and go straight down, where I want to connect it to the 68mm rainwater pipe. I cannot find any form of boss to do this, nor can I find an adaptor to change the size from 40mm to 68mm.

The only bodge I can think of is coring a 40mm hole into the top of the 68mm pipe, inserting the 40mm pipe into this and sealing the joint with black silicone...

Surely there's a neater way?


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A couple of ways perhaps?

There are 32mm to drainpipe bosses available, can the washing machine outlet run in 32?


Or, the standard boss size for a 110mm pipe is somewhere around the mid 60mm's
Theoretically, a 40mm rubber boss adapter could fit into a section of drainpipe branching from a branch connector?



40mm solvent weld boss adapters would be better, but I'm unsure how good the fit to the drainpipe would be.


I hope that gives you some ideas! :)
40 to 68 mm adaptors arent available, for the simple reason to stop people connecting Grey Water into Rainwater drainage. Choices are, either bodge a connection into the rainwater pipe as per your suggestion, or run them separately to the gully.

Reducing to 32mm is not advised, washing machines need a 40mm waste due to the flow rate they pump out at, and any reduction would also be a pinch point for blockages.

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