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We have a somewhat interesting set up under our kitchen sink. There is a flexible pipe fitting connecting the sink drain to the waste pipe. We recently had a clog in the line and I had to disassemble that connection to unclog it. Now that it's unclogged and connected again it's has a small drip leak where the pvc connects to the waste pipe (see pics below).

As you can see, the pvc pipe isn't really secured onto the waste pipe. It was kind of just shoved in there maybe 8 inches. It wasn't leaking before but now that I removed it and put it back it has a slow leak. The last person to disassemble this was a plumber so I'm not sure what theory was on how that connection is supposed to be secured. Did he put some kind of sealant on it maybe? It does feel greasy on the outside, maybe like silicone. Whatever it was, apparently it worked and removing it has done something.

So how do I stop the leak?

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  • Probably should be some type of coupling there, but for now some plumbers putty or silicone sealant should seal it. Clean both pipes well and stuff sealant inside as best as possible and a good rope of it at the joint pressed in.
    – crip659
    Commented Dec 1, 2021 at 16:09
  • FYI, "sealant" isn't a thing in plumbing (thread compound being an irrelevant exception). If you're using goo to stop water from the outside you're doing something wrong. Save it for your siding. @crip659, a compression joint is a coupling.
    – isherwood
    Commented Dec 1, 2021 at 16:47
  • I'd try just tightening the steel compression nut a bit. Start simple. You disturbed it and broke the seal, so make a new one with a little force.
    – isherwood
    Commented Dec 1, 2021 at 16:51

1 Answer 1

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The metal stub from the wall should have a washer inside the sip joint nut (red arrow):

metal stub pipe from wall indicating where the slip joint nut is
Click to embiggen

If your plastic pipe simply slipped in, then either the washer is completely missing or has stretched to the point where it's no longer functional. This is an example of a replacement slip-joint nut and washer:

Slip joint nut & washer
Image courtesy of lowes.com. Not endorsement implied or intended

This one happens to have a red rubber washer. Most of the ones I've used have been some sort of translucent white plastic. I'm not sure which is "better", but they both seem to work just fine. The sloped shoulder of the washer goes toward the pipe being attached to, while the square edge goes toward the nut and is tightened in place as the nut is tightened down.


Bonus suggestion:

To be honest, I'd suggest replacing that accordion pipe with a straight piece. The accordion pleats tend to collect gunk that leads to clogging, while the smooth inside of the straight pipe will collect much less.

To fit the straight pipe in there, you'd have to cut a fair bit off of the tail that goes into the metal pipe stub (you indicated about 8" - that's a lot!). Once that's much shorter, you can loosen the slip joint nuts on the P-trap and wiggle the joints around. I'm willing to bet you could get the trap inlet to line up directly below the drain tailpiece and won't need the accordion at all.

I've installed drain tailpieces with a very slight angle to get a smooth pipe in there and have been able to tighten the nuts down to avoid leakage. I do not recommend it, but it's possible to get away with it if you cannot get a 100% straight line. YMMV... The worst case scenario is that you'd have to reinstall the accordion pipe, but that it would be an almost straight drop down, giving food gunk a far smaller chance of getting caught in a pleat.

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  • What makes you think there's no washer? Could just need tightening, especially after having been disturbed.
    – isherwood
    Commented Dec 1, 2021 at 16:50
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    I don't think the washer is in place and doing its job, @isherwood. Especially if the OP just pushed the plastic pipe in with no mention of tightening the slip join nut. If the washer was there, it was probably pushed down the metal stub as the plastic went in. I've never managed to get one of those washers to "just" slip over the pipe, they're always just a bit tight as one would expect a washer to be in order to make a good seal.
    – FreeMan
    Commented Dec 1, 2021 at 17:07
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    Agree with your answer, but forgive a 'transpondian' question… in the UK I'd have called that a 'compression joint' rather than 'slip joint'. Is that term not used in the US?
    – Tetsujin
    Commented Dec 1, 2021 at 19:05
  • Yes, @Tetsujin, when we're in an elevator, we talk about "slip joint" nuts, while you Brits talk about a "compression joint" on the lift. ;) I believe both are used here, but as the search at this vendor's website shows, "slip joint" is pretty common here. I think most on this side of the pond would consider a compression joint the kind of thing where the nut is permanently attached to a flexible hose, but I'm not a plumbing expert, so don't quote me on that.
    – FreeMan
    Commented Dec 1, 2021 at 19:18
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    @FreeMan - let me just put that info in the boot of my car, then sit on the bonnet ;) I'm no plumber either, but the rest of my family all are/were. I've never heard of a slip joint, only ever compression - anything that gets squeezed in by an 'olive' inside a nut is compression to me, whether the nut is captive or not. Two countries separated by one language… again. Sorry if I occasionally have to ask about these transpondian translations :)
    – Tetsujin
    Commented Dec 1, 2021 at 19:32

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