I'm looking for an underground leak in my condo. I opened up the wall where I know the cold water lines go underground (see picture). I'm going to cap the 1/2 in pipe (the one on the left) and I'm wondering which way to go. I'm no expert but I've soldered copper pipes before.

Option 1: Make a cut in #2 and heat up the join with reducer (#1) to remove elbow and cut section. I have a small section of pipe with a cap that I can solder back in the reducer but as "no expert" I'm worried about too much heat in the T join.

Option 2: Cut big enough section in #2 and cap top portion. Less heat on reducer and T.

BTW if the leak (hissing) sound doesn't go away, after I cap it, I'll have to reconnect the pipe. Option 2 seems the easiest to fix and the one that will put less heat on the T. I'm concerned about too much heat because the solder looks dull and it is about 40 years old. Thanks.

Cold copper pipes go underground close up

  • Option #2 looks good. Have extra space and pipe to play with. Hard to solder/soften solder if water in the pipe. Think they have non solder(push on) caps now also.
    – crip659
    Jan 25, 2022 at 0:39
  • 1
    You should determine whether the old solder is lead-tin solder. If it is, you may have an obligation to not reflow it. Jan 25, 2022 at 2:59

5 Answers 5


Definitely option 2, but with modified procedure:

  1. Using emery cloth or other methods, clean a 2" long section of the 1/2" pipe. Somewhere in the vicinity of the 8-10 inches marks of the measuring tape would be good -- choose a spot where it's convenient to work.
  2. Cut the pipe in the center of the cleaned section.
  3. Deal with the water that spills; remove water from the standing section of pipe to at least 4 inches lower than the cut. (Open a drain point below this level, or suck water out of the pipe with a drinking straw, wet/dry vac, absorb it by inserting a rolled paper towel or cloth, etc.)
  4. Pry pipes laterally as needed to get the cap(s) in place and soldered. If the cap is just for test purpose consider using a push-on ("Shark-bite") rather than soldering a cap. If the pipes don't have enough give then reflow the solder at the elbow going into the reducer and tee so that you can swing the vertical leg out a bit.
  5. When you're ready to re-join the pipe use a "no-stop coupler." A normal coupler has a ridge, a dimple, or other feature that allows it to slide onto a pipe only until the pipe is halfway through the coupler. A no-stop coupler does not have this feature -- it's maddening for ordinary work, but it's a miracle for repairs like this! Slide it fully onto one leg of pipe, align the pipe ends, slide the coupler back until it's centered across the joint, and hold it there until the solder cools. How you accomplish that on a vertical pipe is left as an exercise for the reader -- but it probably involves an assistant with pliers or other tool holding the coupler in place while you work.

The photo below is from Water Pipe Replacement at familyhandyman.com. comparison of stop and no-stop couplings

  • people often put some soft bread in the pipe just to absorb any stray bits of water -- it dissolves eventually. Also, the no-stop fitting tends to be pretty tight, so no real need to have an assistant hold it.
    – gbronner
    Jan 25, 2022 at 4:18
  • I've tried the white bread in the pipe trick. I could never get it to work. However, I'm no professional plumber with mad soldering skillz either.
    – FreeMan
    Jan 25, 2022 at 14:52
  • This was my first choice because I had all the fittings until I realized I didn't. That elbow is not like the ones I have. Then I don't have all the fittings for option 2 either so I have to go to the store anyway. I'm doing it your way. I'll get the weird elbow and reducer for the reconnect. I can return them if I have to keep the cap in place. BTW I use a shop vac to drain the pipes. Thanks.
    – Rodo
    Jan 25, 2022 at 17:09
  • 1
    @Rodo The weird one is a "street elbow." Now that you've seen one you'll notice them a lot more often; they're not so weird after all. :-)
    – Greg Hill
    Jan 25, 2022 at 18:00
  • If you only get rid of the water from the closest 4", you'll still have more trouble than normal with the soldering. Aim for more (e.g. suck it out with aquarium hose if it's clean water). On one awkward repair I had to get a helper to heat the pipe with a heat gun near where the water was standing, while I soldered the joint, partly because I couldn't heat the copper very evenly with access only over a very narrow angle
    – Chris H
    Jan 26, 2022 at 11:37

The 40 year old solder when heated back up to melting point will act like it is brand new. The trouble will be is, its surroundings are not new. The tarnished copper needs to be cleaned back to bare copper. The solder too. You will still need to use flux. It is also best not to reuse the old fittings only because the original solder really make it difficult to join or rejoin anything together. If there are any impurities left on any surface it will contaminate any solder joint done. You will still have to deal with left over water in the lines as well. You can drain the lines until they drip no more, but as soon as you heat the pipe up, more comes out. This can happen again and again. Opening a valve at a sink will help minimize this, but it still will happen . So be expecting it. Be thrilled if it doesn't, for it can be frustrating

Back at the reuse of old fittings. Again it is best to not reuse, in some cases you must. I know I have had to. Since the solder will not fall out on its own, and it is clean, as in no contaminates, the fitting can be heated up and with flux on both parts slide them together while the solder in the joint is fluid. This makes it sound really simple, but for me it has not been, but it can work.

Unless you plan to use acetylene, I don't think you need to worry about too much heat. It will discolor the pipe, but it should do no major damage. If it takes too long for a pipe to het up, suspect water in the pipe to some degree. It does not take much.

  • 1
    "This can happen again and again." Boy howdy can it!
    – FreeMan
    Jan 25, 2022 at 14:53
  • I always wonder why they said not to reuse old fittings. Now I know it is because they're hard to clean. Thanks.
    – Rodo
    Jan 25, 2022 at 17:01
  • I would also be worried with 40 year old joints that the solder may be lead based. AIUI lead free solder formulations don't handle lead contamination very well. Jan 25, 2022 at 19:30

"too much heat" is when you burn a hole in the pipe, other than that it's not a thing.

Un-soldering a fitting is always a pita and a crap shoot.

Cut the pipe somewhere where there's no solder drips in the way, and put your fitting there.

Where #2 is pointing at 8.5" on your tape is a good spot. That leaves enough to cut your cap off later and still do something w/o having to mess with the reducing tee.

  • 1
    Propane you can't really go wrong. MAPP gas you might if you try hard enough. And with an oxy-acetylene torch you'd better know how to use it or you will burn holes.
    – Mazura
    Jan 25, 2022 at 4:03

I'm going to cap the 1/2 in pipe (the one on the left) and I'm wondering which way to go.

Cap it permanently or just in an effort to track the leak?

If temporary then use a push-to-connect cap such as this:

Sharkbite half-inch push-to-connect brass cap

I would:

  • Cut the pipe far enough from any solder joints
  • Deburr and ream the pipe
  • Cap it off with a push-to-connect
  • When you're ready to put it back in service then hopefully you're far enough to solder a coupling

Since this is behind a wall I would not leave a push-to-connect fitting as a permanent solution.

  • +1 Good method to use on your detailed part of the question. Something I overlooked.
    – Jack
    Jan 25, 2022 at 15:06

The other answers seem to miss using a flux.

Once you have cleaned the copper pipe, and fittings, to bright and shiny then apply a flux.

I have two types: one ordinary strength used for most work.

The stronger one gets used for re-work like this.

Make sure both are cleaned off thoroughly when finished.

The flux makes the solder flow easily around the joint.

I will also add that some countries require using lead free solder for potable plumbing and that requires a different flux as the solder melts at a different temperature, and if you have done lots of plumbing soldering then you can see & feel the difference.

  • 100% agree, but this would be better as a comment, since it doesn't actually answer the question.
    – FreeMan
    Jan 25, 2022 at 14:54
  • True that, I thought about, it is absolutely needed, but it never made it into my answer at the time
    – Jack
    Jan 25, 2022 at 15:04

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