We've had a new extension added to the house which has a drain under the concrete. We're left with a 110mm (I think) vertical pipe which our waste needs to go down inside the extension.

This waste is only for the sink and dishwasher. Toilet and bathrooms go down a waste pipe at the other end of the house and meet on the main sewer pipe which was sorted by the builders.

  • How do I leave the connection between the 40mm from the sink to the 110mm?
  • Do I just drop some of the 40mm inside the 110mm pipe so that it can drain away?
  • Does the connection need to be blocked off with a rubber seal to stop smells?
  • I assume if I do need to seal it up that I'll need to have a T joint or similar above so that it can be unblocked if necessary.
  • After some more reading, do I need to install a boss pipe on top of the current pipe in the ground which would have the 40mm coming in to it then that would have access from the top/side depending on the boss pipe type.
    – jamestsymp
    Jun 7, 2019 at 13:06

1 Answer 1


You want something like this.

rubber drain connector 110mm-40mm

This is a rubber connector which goes in the top of the 110mm pipe, and the 40mm pipe slides in to it.

Yes, the connection needs to be sealed to seal off smells. If the 110mm pipe gets blocked (unlikely, because any blockages are much more likely to form in the 40mm pipe), you can easily disassemble it.

Note: The link is to Screwfix because that was the first result I found. I wouldn't actually buy from Screwfix.

  • Thank you. This was what I was originally trying to find but failed hopelessly so assumed I'd been looking for the wrong thing.
    – jamestsymp
    Jun 7, 2019 at 14:34

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