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After being away from the house for a week, we had the unpleasant surprise of returning to a note from our housesitters about a leak under our sink. The whole bottom of the cabinet had a layer of water on it, and the tupperware in the image was completely full. Unfortunately we had the bad practice of storing things in the cabinet so the view of this container was obstructed--I hadn't looked at it since we moved in years ago (it was put there by the previous owners, presumably).

The two elbows are connected with what I assume is pvc cement and are sitting at an odd angle due to the imperfect spacing between the upper sink connections and lower drain pipe.

view under sink showing leaky connection

There was a ring of what looks like plumber's putty around the connection, which was obviously doing nothing but is a sign of an attempted fix. Photo of it after removal:

putty after removal from pipe connection

My original intention was to remove these two elbows and replace them, so I went to take a look at the rubber connection at the bottom of the photo. This had two pipe straps around it, but I removed them before taking the photo.

enter image description here

I had assumed the rubber junction was also being used to stop a leaky connection, but it turns out it's actually being used as the connection itself, and is just pipe-strapped around the elbow and drain pipe. After removing the straps and sliding the rubber up there was a lot of junk (from where it was acting as a pipe), but there are no signs of leakage outside this connection.

For further context, this is an older home (1950's) and the previous owners had a kitchen remodel done (~5 yrs ago). So, my read of the situation is: when the cabinets were installed the plumbing was done hastily--this double elbow was installed to get close to lining up with the existing white pipe, and the rubber junction was used to fudge the alignment error. Struggling to get the alignment right, they twisted the piece and caused the cement in that next junction to develop small cracks which caused this slow leak. We neglected to notice this slow buildup over time, and the timing of the overflow unfortunately coincided with a time we were not home.

I had hoped to be able to replace the lower white pipe with one of the correct length to allow a clean connection to the rest of the system, but on further investigation it looks to be inaccessible without destroying the bottom of this cabinet (there are several elbows in-between this piece and the ultimate drain in the crawlspace).

  1. Is it a good idea to apply some silicone sealant around this leaky connection? My understanding is that it would hold up over time (unlike the putty), and these pieces will never plan to come apart anyway. Or should these elbows be replaced?
  2. Is there a better way to connect this system to the white drain pipe? The rubber junction seems to be holding up fine for now, but it feels dodgy especially because a leak here would go under the cabinet and go undetected for longer, and with less evaporation.
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    However you do this, I'd suggest getting it up to code, because at some time you will want to sell the house, and it must pass inspection. Yes, a quick fix with silicone might last a year or two -- or not, but you'd be living with a sword of Damocles dangling. Mar 30, 2023 at 2:36
  • Which raises the question how this made it through inspection when we bought the house a few years ago. Fair point though. Mar 30, 2023 at 3:02
  • How much vertical pipe can you see below the cut-off fitting, i.e. below the bottom of the cabinet? You might be able to use an oscillating tool to cut the fitting off, and properly slip a PVC coupling on the pipe, which would allow you to extend the useable length upward. Then replace all the junk drainpipe and use a shielded Fernco for removeability.
    – Huesmann
    Mar 30, 2023 at 14:57
  • Also, it looks like the installation was done using an unshielded Fernco that was the same diameter on both ends. Since the fitting was left on the drain pipe, the Fernco had to be larger than the pipe diameter, and guy filled the gap on the top end with putty. Total hack job, when you can get Ferncos with different sizes on each end.
    – Huesmann
    Mar 30, 2023 at 14:59
  • It's leaking from the circled red elbow? Did you figure it out? :)
    – rogerdpack
    Nov 8, 2023 at 4:12

2 Answers 2

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If you are ambitious and seeing the bottom of the cabinet is damaged, you could cut out the bottom of the cabinet. This would allow you to repair the plumbing properly. You would then be able to replace the bottom of the cabinet with a new piece of plywood. I've done this a couple of times when I had an undetected leak under the sink that ruined the bottom.

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  1. NO. Do not attempt to "fix" this with any sort of caulk (silicon or otherwise) or putty. That's just as much of a kludge as the original fix.
  1. YES. The original drain pipe was cut off flush at the hub by an incompetent "plumber" who left himself no options but to use that rubber "Fernco™" boot. You will need to fix this up in order to do a proper fix, though Ferncos are allowed by code.

enter image description here

The red arrow is pointing to the remains of the white PVC pipe that is still cemented inside the hub leading through the floor of the cabinet. Since the old pipe is still inside the hub, it's impossible to install a new one, and since it was cut off with no pipe sticking out, there's nothing left to attach any new fittings to.

You might be able to ream the old pipe out of the hub using a "hub saver" (or "socket saver"). Here is one example (a result of a DuckDuckGo search) of what one looks like:

enter image description here
Source: SupplyHouse.com no affiliation or recommendation intended or implied.

You use the "socket saver" in a drill to cut out the old pipe from inside the hub without damaging the hub itself. You can then glue in a new piece of pipe. You will need to ensure that the socket saver is in line with the pipe you're drilling, as I'd imagine that you could damage the hub if you're not careful. However, the central disk is designed to keep the bit centered in the pipe. I've never used one myself, so I don't know all the ins, outs, and caveats for using it, so caveat emptor.

Once you've got the hub cleaned out, you can install new plumbing. I'd suggest that you'll need to figure out how to disassemble the joint at this red arrow, then install the new plumbing changing the angle of the pipes slightly from approximately the yellow line to the green line.

enter image description here

The goal is that the end of the green line will be directly above your white stub of plumbing coming up from the floor.

Additionally, since this is a cabinet that will eventually (possibly sooner rather than later after the water damage) need to be replaced, it's often recommended to use screw together fittings under the sink instead of glue together fittings.

If at all possible, I'd suggest glueing a stub of 1-1/2" PVC into the white hub in the floor (it looks to be 1-1/2", measure to be sure), then using screw together fittings from there all the way back to the rest of the plumbing. Using screw together fittings will make it much easier for an amateur plumber (like you and me) to get everything angled correctly before tightening. If you use glue together fittings, you have to dry fit, mark then glue and ensure that your connections are lined up exactly on the marks. This can be rather difficult and may end up in wasted fittings that have to be cut back out (source: personal experience doing DWV plumbing for a new house addition - at least you're not throwing away 3" fittings!).

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    Actually, it looks like the previous numbnuts cut right through a fitting —see the ribs? Probably because he needed something sticking out the bottom of the cabinet to slip his Fernco onto!
    – Huesmann
    Mar 30, 2023 at 14:52
  • That's true, @Huesmann. One would hope there's enough depth left (1/2 the pipe diameter) to securely glue a new piece of pipe into. If not, will probably have to remove the floor of the cabinet and do repairs below that.
    – FreeMan
    Mar 30, 2023 at 15:20

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