The reverse osmosis filters waste clamp (40mm) doesnt fit on my waste pipe (50mm)

I ordered a 6mm compression fitting to use an npt taper

The compression fitting took 3 weeks to arrive and I'm trying to measure the male end its maybe 9mm In inches this comes at 0.35 I cannot find an npt taper size for this I cannot find a 50mm waste clamp

Please help, what can I do?

Edit: under my sink

As you can see the original U bend is 40mm but too short with no space for the clamp


This is the 6mm elbow compression fitting I have


I ordered this because I feel 3/8inch is the closest to the size of the compression fittings thread size

Should I order "pvc cement" incase it is a bit loose?

  • The waste line is metal or plastic? Standard under sink pipe/drain set-up?
    – ojait
    Commented Jan 10, 2021 at 16:46
  • pictures, please. Commented Jan 10, 2021 at 17:43
  • Plastic, photos and more info added
    – Lankyjack
    Commented Jan 10, 2021 at 20:33
  • That's he dishwasher drain hose attached on the left?
    – ojait
    Commented Jan 11, 2021 at 3:34
  • If you mean on the right that's the washing machine
    – Lankyjack
    Commented Jan 11, 2021 at 6:54

1 Answer 1


I ran into a similar situation and not being able to locate the correct sized part (saddle) I successfully installed a hose barb fitting

enter image description here

Looking at your photo I can't easily find an acceptable location for a threaded barb fitting. Ideally it should be oriented vertically and on top of any pipe section. And obviously before the trap.

If it's possible to add a short extension of pipe to the connection where the flexible hose is attached so as to allow an attachment point that would facilitate connecting the new fitting.

Installation is a simple matter of drilling a slightly undersized hole and forcefully turning the fitting into it after wrapping the threads with Teflon tape.

  • Is before the trap on the Tee with the barbed elbow compressor not acceptable? I also have a straight I guess I could put it in vertically after the trap but not sure if my drill will fit in that area, is the pipe at the bottom underneither the flexible attachment really not acceptable?
    – Lankyjack
    Commented Jan 11, 2021 at 7:08
  • I would guess positioning the fitting in any orientation but vertical might potentially allow contamination (I'm not 100 % sure about this). Also, theres a greater risk of flow restriction and blockage due to the fitting threads being partly installed inside the pipe. A vertical placement decreases that happening. Again, I'm going by instinct and not quoting plumbing code.
    – ojait
    Commented Jan 11, 2021 at 14:41

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