38mm European waste pipe to 40mm UK compression waste fitting

[Ian2000]

What's the best way to ensure a watertight fit connecting a 38mm European / continental waste pipe to a 40mm UK compression waste fitting without using a 38mm to 40mm adaptor prior?
The reason not to use an adaptor is because there is no space.
Note, a 40mm compression fitting on a 38mm pipe will hold however the joint won't be as tight, both mechanically and water pressure. Hopefully there is a way to improve the seal.

 

[kidgreen61]

A 40mm compression coupler will do the job

 

[Madrab]

A little self amalgamating or denso tape around the pipe to make it a little tighter, if you feel you need it.

 

[Ian2000]

Hello kidgreen61, Yes I've noticed a UK 40mm waste compression fitting will work on 38mm waste pipe however understand it puts stress on the plastic compression olive as the plastic nut needs to be overtightened, greater than the manufacturing designed spec. Also, I noticed when trying, it's easy to accidental pull out during installation as of course there's less friction between the compression olive and the pipe, also increasing the risk of leaks. It has been an issue where the joint can't be seen to check for leaks after installation.

Hello Madrab, By self amalgamating or denso tape, do you mean wrap either tape a few times around the waste pipe where the plastic compression olive is located to increase the thickness of the pipe by a few mm?

38mm - 40mm waste conversion fittings do exist however I don't have the space to install it.

 

[denso13]

Yes I've noticed a UK 40mm waste compression fitting will work on 38mm waste pipe

A good quality multiifit connector, such as McAlpine will be fine. They are designed to fit different diameter pipework including copper and lead.

 

[Madrab]

wrap either tape a few times around the waste pipe

Yes, where the rubber seal will sit. Both tapes once attached to each other and the pipe are waterproof and will take up the couple of mm, if you feel you need it.