Need to lay condensate pipe from the boiler room to the waste pipe, on the other side of my flat. Will use condensate pump and use loft as proxy.

I want to drill through ceiling from my boiler storage cabinet into the loft, lay the condensate pipe under the loft floor and towards the waste pipe that extends to the roof and goes down to the bathroom.

When I reach the waste pipe in the loft, I think I have these options:

  1. drill a hole in the waste pipe in the loft and inject condensate pipe there. But it would mean it’s going to be above the vent pipe. Which ends in the bathroom below. As marked on the picture

  2. drill through the loft floor into the bathroom downstairs and put the condensate pipe through that hole. Then lay it next to waste pipe until I reach below the vent pipe and drill condensate pipe into waste pipe. Blue version on the picture

  3. drill hole in the waste pipe itself, in the loft, and put the condensate pipe inside the waste pipe, and lower it down until it reaches a point below the vent. Option red on the picture (imagine red line is inside the waste pipe)

Do I have to end condensate pipe below the vent pipe? If not then I can just attach it to waste pipe in the loft as per first option, simplest. If yes, which of the other 2 options above is most sensible?

enter image description here

  • As long as the drain is below the condensate pan it does not matter. The register passes conditioned air which is or will be passed over the condenser by the fan. Be sure to vent it.
    – Gil
    Jul 12, 2021 at 20:10
  • Drilling a hole into a drain like is a guaranteed way to generate a life-long leak that will, eventually, have to be properly repaired. Use proper plumbing fittings to joint the condensate line to the rest of the drain system and do it right the first time.
    – FreeMan
    Jun 23, 2022 at 13:48

1 Answer 1


Use an appliance "wye" installed in an existing drain line, that way the water flows on an angle downward.


Holes in drain lines don't pass inspections. https://inspectapedia.com/aircond/Condensate_Drains.php

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