There is a small crack in this drain pipe, and it's so thin there that I can bend it with my finger. The section that's palpably weak is no more than an inch long. The crack is exactly where the drop of water is in the top picture (just left of the Y, on the bottom of the pipe).

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This section is hidden behind a finished wall in the basement. It runs into an unfinished area soon after and is visible from there too. There's about 30 feet of pipe in the unfinished area that is all fine on visual inspection and nowhere that I pushed on moves like the little bit where the crack is.

There is roughly 8 more feet behind the wall before it exits the basement to the street. I'm obviously not thrilled about taking out the entire wall to the room to replace pipe if it's in good shape like the sections in the unfinished area. Is there a chance the section that's leaking has seen increased wear because of the Y junction just before it? If so, it seems reasonable to repair it and leave the rest as is. Is that a good call or should I replace more than that?

What is a good way to patch this section given that I don't have much space for access without ripping out studs in the wall in front of it? The piece of wood above the pipe is a support for the stud that drywall is attached to in the room.

  • I assume rustoleum leak seal tape is not a robust long term fix. Just brainstorming possible easy ideas.
    – Evan
    Mar 21, 2020 at 0:52

2 Answers 2


That's a bad spot to have a leak. That could have been caused by too much heat from a torch or excess acid flux. You might be able to cut the 1 1/4" pipe on the other side of the support and heat the joint going into the "y" and remove the piece of pipe. Then clean out all the old solder by heating up the pipe and wiping out solder. Use emery paper to clean the surface down to the copper. Get a new piece of pipe and a repair coupling. Slide the repair coupling on the old pipe after fluxing and then slide the pipe into the "Y" after applying the flux. Flux the new pipe and slide the repair coupling into place. Now sweat the "Y" and the repair coupling. You should be good to go.

  • 1
    That's the way to do it. The other point is to try to keep it dry inside until you get it sweated on - especially if there is any trickling water coming in. Since it's a drain and not a supply line there'll be no problem with pressure from steam but still probably a good idea to use a little wad of bread above the repair.
    – HoneyDo
    Mar 20, 2020 at 22:29
  • I like that idea of it being caused by the original work in that area, and the plan for repair. Thanks!
    – Evan
    Mar 20, 2020 at 22:41
  • Why not just replace the entire copper Y section with DWV PVC(?) and tie it into the remaining copper with flexible couplings?
    – SteveSh
    Mar 20, 2020 at 23:22
  • @SteveSh Flexible PVC fittings behind a wall is looking for trouble. You've got good copper might as well use it. Just my humble opinion.
    – JACK
    Mar 20, 2020 at 23:29
  • 1
    @Jack - Oh no, I wasn't referring to those. I meant the heavy rubber couplings with the screw type hose clamps.
    – SteveSh
    Mar 21, 2020 at 1:15

While there are various possible causes (aside from not cleaning acid flux properly, the one that comes to mind in that location is improper/insufficient support causing a bending force on the pipe from the Y junction) I personally would replace as much as possible with PVC (and take your copper to the scrapyard.)

If you are prone to consider that going overboard, please check the pH of your water. If it's acid, that's not going overboard, it's saving you future hassle as more places rot through, one by one, and then leak until you notice them.

Soldering copper supply pipe is a relatively easy skill, though many folks these days seem daunted by it. Personally, I can solder them just fine but I won't be buying new ones in the age of PEX, especially with the price of copper so high. Drain pipe, simply due to the size, is much more difficult to solder well, especially with typical homeowner torches. PVC is an order of magnitude easier to do right, and it is unaffected by water chemistry.

Additionally, new copper pipe and fittings in drain pipe sizes are painfully expensive, especially when you may need to buy 10 feet even if you only need 6 inches of pipe.

Do NOT throw out copper scrap, it will probably pay for your whole replacement pipe and then some.

  • I was wondering about bending force too. There's a hanger on the pipe just to the left of the picture. But I do wonder whether the wood support at the top is actually applying pressure to the pipe here. I'll have to cut that stud out to access this for the repair anyway, and won't be putting it back right on top of the pipe like that.
    – Evan
    Mar 21, 2020 at 0:46
  • I'm putting this to community wiki status since @GeorgeAnderson mentioned acid water as a concern first, though that was not a factor in my response. As I've said before when choosing that, I sure don't need the "points"
    – Ecnerwal
    Mar 21, 2020 at 1:34
  • 1
    I'll definitely be testing my water pH. Haven't yet. Just looked on the right side of the y, and there is nothing supporting that pipe for a while. Can't decide if the vertical pipe is a load or support, it's not attached to the wall in any way, so I have a hunch it's not a support.
    – Evan
    Mar 21, 2020 at 1:40
  • Not thrilled with the various shades of green on the pH test kit I got, but I think it's fair to guess that it's somewhere between 6.5 and 8.
    – Evan
    Mar 23, 2020 at 1:37

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