I recently moved and I have a water filter that I'm trying to install under my sink. I'm used to flex lines, but this place has a piece of copper pipe running straight down from the cold water knob to the shutoff valve. There's a compression fitting on the shutoff valve, but I can't remove the pipe as it's screwed into the faucet above and I don't have a basin wrench. Additionally, I'm not sure if there's any soldering that goes on there so even if I buy one I don't know if that is another roadblock. Trying to figure out what I need to acquire to do this, and if I end up having to cut the tube or the like, what sort of connectors help me attach a flex line to the existing copper tubing.

Also is there a way to know the sizing of things from the diameter of the nuts (e.g. if I do get the copper pipe removed and can just slap a flex line in there, I need to know what size the threads are. It would be nice to not have to make a bunch of separate trips to the hardware store)?

1 Answer 1


I'd use a tubing cutter or hacksaw (gently!) to open a section in the supply pipe wide enough to comfortably work. Use emery cloth or other tool to debur the cut end. Now use slip-on connectors (like SharkBite) to attach your flex lines.

  • 1
    When you go to the store to get the parts take a photo with a tape measure behind the pipe so you get the correct size. Sharkbite type fittings will be easiest for a novice. +
    – Ed Beal
    Aug 20, 2019 at 14:57

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