What is this closed off pipe under my kitchen sink?

Question

This pipe has a very slow leak. What is the pipe for and what is the best way to stop the leak?

Answer 1

It is a drain cleanout. You can try turning it clockwise to see if it tightens enough to stop the leak. If not, have a bucket or pan to catch any spillage, turn it counter clockwise, remove the plug, clean it off and the inside of the pipe. Wrap some Teflon tape around it and screw it back on.

Answer 2

There's no way for us to know; it is unusual. Possibly your drain was re-configured at some point, and that closed-off pipe is an old drain which had some trouble.

I guess your real question is how to stop the leak? Unfortunately, if that pipe is full of waste water, opening it may cause a mess; so be prepared for that -- have a bucket that can fit under it, shop vac ready, towels, a pair of waterproof gloves, etc.

I'd open the seal using a pipe wrench, drain it, then apply pipe joint compound, often called pipe dope to the threads of the plug, then screw it back in. That should stop it from leaking. The pipe joint compound is a waterproof compound that forms a gasket-like seal to stop water from leaking out of clean-outs and similar seals.

If the above doesn't fix the leak, the threads of the plug or pipe could be damaged; but that's unlikely, the fresh pipe dope will probably fix the problem.

Answer 3

From the perspective of your photo it looks to be perfectly in line with your drain pipe. So it appears that this is another tap into that line. Perhaps it wasn't in the right place and rather than remove it they just stacked another one on top of it.

If it's leaking out of the cap, you should be able to remove that, use some thread sealant on the threads and reinsert it. If it's leaking out of the joint behind the cap, then you may need to do some additional work to cut off the bad joint and fix whatever is going on there. You may need to open up the wall to get to what you need to get to in order to fix this properly.

If this were mine, I'd likely get rid of this mess entirely. There is no purpose for this extra drain now and it's, as you can see, causing issues.