I was unclogging a blocked drain and putting everything back together and I'm unsure how this piece is supposed to work

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Here it is just loosely resting where it came from. It seemed to be held onto the pipe by some cohesive force before (though now I'm doubting myself about that), but I'm not sure how. I thought I may have lost a washer or something but I double checked the floor and couldn't see anything.

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Here's the rest of the plumbing without that piece

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And here's how I left it for now

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While the metallic piece is screwed on as before, I'm pretty certain it's not accomplishing anything (besides maybe aesthetically). Something presumably needs to exert a force towards the wall to get a tight seal there. It expectedly leaks slightly. If I apply pressure towards the wall then it doesn't.

The sink was leaking before this, but I thought that was only from the black rubber washer. It's possible that my landlord never did it properly and that it always leaked from here too, but I tend to think I'm missing something.

How can I fix it?

9 Answers 9


Agree with others. In UK known as a compression fitting. You're missing the black rubber o ring.

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  • In the US, that part may not necessarily be rubber, but it does the same thing
    – Machavity
    Mar 16, 2020 at 17:08
  • @Machavity: In Germany, we typically use a medium-soft (in between rubber and the plastic of the pipe) type of plastic. The siphon side needs to be one meant for such a compression fitting, though. Mar 16, 2020 at 21:12

That nut with the blue plastic ring is designed to squeeze the ring around the metal pipe stub and the edge of the trap piece that goes around the outside of the metal piece. For this to work effectively the metal stub pipe has to slide inside the piece from the trap about an inch or so. (That is why the other answer suggests that the metal stub pipe may have pushed into the wall too far).

If the plumbing is old it can be a good idea to purchase replacement rings like that blue plastic piece. Old rings can get hard and brittle. Some of the better versions of the rings that you can buy are made of a more rubbery and pliable material than others. They will squeeze into place better and make a better seal than the old hard plastic.

While you are at it consider removing and inspecting the ring seal in the nut that faces the wall. It may need replacement as well.

  • If running warm water doesn't get me another quarter turn to stop it leaking, then I must have used an old o-ring (or it's the wrong type in the first place).
    – Mazura
    Mar 15, 2020 at 22:10
  • I don't think the stub pipe from his wall is metal, it looks more like chrome plated plastic where the chrome is wearing off. Mar 17, 2020 at 17:10

I suspect you may have pushed the sliding bit of pipe a bit further into the wall connection so there's no pipe left for the nut to clamp the ring onto now. Try pulling it out a bit (you may need to first loosen the wall-side nut) so that more projects towards the trap piece.


If the white fitting is chamfered on the inside (where it meets the metal) then it's supposed to have a V-shaped o-ring. If so, the o-ring is incompatible. At the very least, that's not the nut that came with the trap.


It's a compression fitting.

I call them McAlpine fittings as that's the name of the fittings I use. You're missing the rubber washer which goes on after the blue compression ring. This is what causes the seal when you screw the nut.

Looks like 1.25" could be 1.5".

  • 1
    Thanks for the answer, and welcome to Home Improvement!
    – IronEagle
    Mar 16, 2020 at 13:41

Nobody has mentioned it yet, but these are called slip joint fittings and they can be a real bear to install: too tight and you risk stripping threads, distorting that rubber washer, or other bad stuff... too loose and it's obvious what happens.

Plumbers find them mildly irritating, but they usually have the magic touch needed to get them installed just right. I don't have the magic touch. You probably do not have the magic touch, either. So when you finish reinstalling/replacing it, watch it for a few days to make sure it's not dripping.

I'd go pick up replacements for the white nut, the rubber ring inside it, and maybe for the piece of pipe that is sticking out from the wall side of the drain pipe. It'll only cost a few bucks, and it's much easier than fighting with old and worn out parts.

When you install it, put on some work gloves to get a good grip; you might need to turn it a little harder than you think. And as another poster mentioned, make sure there is enough of the plastic pipe coming out of the wall side to give the nut something to grab onto.

  • Being a chemist, I largely replace the magic touch by applying my secret chemical (aka a drop dishwashing soap). Mar 16, 2020 at 21:10
  • 1
    I had lots of trouble with slip rings until I started buying plastic instead of metal. The plastic ones have some give in every piece and seem to seal better. The other problem for the inexperienced is that there are two similar looking installations. One nut is intended to go around the outside of a pipe and seal the gasket to the outside. The other is intended to go on a pipe with a flange on the end and mate with another pipe that has threads on the end. They look the same but are different sizes. Unless you buy a complete set you will probably find yourself..... Mar 17, 2020 at 5:01
  • 1
    wanting one kind of pipe when the other is the right one. A complete set is only a few dollars in plastic so get it instead of individual pieces. Mar 17, 2020 at 5:02

The rubber seal has probably been pushed into the slip joint in the trap. Check to see if you can see it once the trap has been removed. You will need to fish it out with a small flat screwdriver


I think you are missing a component.

In addition to the slim plasic ring (blue in your picture, but the color varies) there should be a much thicker rubber ring (black in my experience) which has a chamfered fitting to fit into the pipe fitting (trap in your case) and a flat face against which the nut presses (via the slim plastic ring).

This thick rubber ring is compressed by the nut and as it is compressed the hole in the center of the ring shrinks. It is this shrinkage of the hole that grips and seals the pipe.


After fitting everything tight and solid put some plumber putty around connection before putting nut on and tightening should take car of drip

  • 1
    You should not use plumber's putty here. The proper rings will prevent leaks.
    – Machavity
    Mar 17, 2020 at 13:46

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