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This elbow joint is leaking. I think it’s the condensation pipe off the boiler because it seems to leak when the boiler comes on. I’ve tightened it fully but still leaking.

enter image description here

The pipe on the left (white) measures 21.5mm and the grey pipe coming out of the waste pipe seems to measure 29mm

The angle is 90 degrees and it looks like a compression fitting, but i can’t seem to find this elbow joint anywhere

Extra details: This is located under the sink. The boiler is located to the left on the wall. This pipe comes out the bottom of the boiler. The big pipe in the middle going down is the waste pipe

Washer: Looks like a rubber tapered washer. Outside diameter about 28.6. Inside diameter 21.5 height 6.5 enter image description here

Conclusion Actually someone said to check the water isnt leaking from the white elbow joint and running down onto the grey nut.. once I checked it, it was obviously leaking from the white elbow joint, so I ended up sealing up the white elbow

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  • Is this under a sink? Have you tried undoing the gray plastic nuts and looking to see if there is a washer inside that needs to be replaced? Where exactly is the leaking happening?
    – Armand
    Commented Apr 3, 2022 at 17:35
  • Which is the "pipe on the left" (there are 2 white pipes), and what part of the grey pipe is 7.5mm bigger than it? Which is a waste pipe? Where is the boiler? Are these supply lines to a sink somewhere? Have you looked at the boiler to identify the condensate line and tried following it through the house to confirm that this is it? Should the picture be rotated 90° to the right so it's right side up (the lettering on the bottle seems to indicate that it should). So many questions, so few details...
    – FreeMan
    Commented Apr 3, 2022 at 17:52
  • Sorry I’ve added extra details. This is located under the sink and the leak is happening at the joint on the left small white pipe into grey)
    – User1
    Commented Apr 3, 2022 at 18:12
  • I haven’t undone it yet as I don’t want to break anything before being able to replace it. I think the boiler is 10 years old so it stands to reason that this joint (and the washer, if there are any) are also 10 years old
    – User1
    Commented Apr 3, 2022 at 18:13
  • Can you post photos of vertical waste pipe junction, the thin white incoming pipe end, and the gray elbow, now that you've removed the compression nuts?
    – Armand
    Commented Apr 4, 2022 at 21:11

2 Answers 2

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I suspect the elbow is just part of the "elbow plus tap into drain" unit that seems to have been spliced into the drain pipe. Here is a photo of a part with similar function:

(It is called "Drain Waste Trap Pipe Extension Connector 1 1/2" BSP with Dishwasher Input" so if you search for a similar fitting you may find your elbow included as part of a similar whole unit.)

enter image description here

It looks to me like a black compression washer is visible down between the pipe and nut as shown by the arrow below. I would think its inner diameter would match the outer diameter of the gray pipe going into the nut. Similarly, I would expect a compression washer in the other gray nut that fits around the thin white pipe going into it. You should be able to purchase such washers based on your measurements and the assumption that they are standard rubber compression washers.

enter image description here

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  • I’ve added a photo of the washer. I can’t seem to find any 21.5mm tapered washers though. Is this a thing?
    – User1
    Commented Apr 4, 2022 at 16:13
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    @User1 Try Jay's suggestion of undoing both big gray compression nuts, cleaning off the rubber washers and the elbow and any other gunk you see, and reassembling, alternating slow tightening on the nuts so one doesn't pull the elbow out of alignment for the other. When you check for leaks at the white pipe/elbow junction, check to make sure water is not leaking out of the white pipe a bit upstream and running along the outside of the pipe, only to drip once it reaches the gray nut. A tiny trimming of the thin white pipe end may be necessary; the washers if still pliable are likely OK.
    – Armand
    Commented Apr 4, 2022 at 21:23
  • you were 100% correct that the water was actually leaking from the white elbow joint and running down onto the grey nut.. Sorry I'm quite new to this, it's so obvious now you've said it though!
    – User1
    Commented Apr 6, 2022 at 7:07
  • Glad you solved it - we learn by doing!
    – Armand
    Commented Apr 6, 2022 at 8:02
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It looks like the downstream end of the elbow fitting is misaligned and under stress, making it hard for the washer to do its job. I've shown it exaggerated at "a" in the picture.

You would fix this by loosening the two compression nuts shown and if possible, if there is one further down the long white pipe, that too.

Align everything as best as possible before retightening. You may need to insert "b" further into the coupling or to cut it half an inch shorter if it's bottomed out. You may need to shorten pipe "c" by cutting out a piece and replacing with a coupler (but first see what can be done further along it outside the photo).

enter image description here

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  • That's a good point, but I would be leery of undoing the screws initially, for fear of not being able to re-establish a good seal to the vertical drain pipe.
    – Armand
    Commented Apr 4, 2022 at 21:09
  • You would be right ! Try first to correctly align and remove stress from all joints by loosening everything except those screws. In fact, I was thinking you might need to rotate that 4-inch clamp a little but you could achieve the same thing by cutting and shortening the long white pipe, which would be a lot less risky.
    – jay613
    Commented Apr 4, 2022 at 21:13
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    Or .. better yet ... where the white pipe is inserted in the grey compression joint, when it's all loose you might insert it further and if it bottoms out, just shave half an inch off its end. That might be enough to correct what I see ... if that's even the problem.
    – jay613
    Commented Apr 4, 2022 at 21:15
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    I modified the answer to reflect the above comments.
    – jay613
    Commented Apr 4, 2022 at 21:31
  • Very nice! Too bad I can't upvote your answer twice. :)
    – Armand
    Commented Apr 5, 2022 at 0:16

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