My main water shutoff valve inside my house needs to be replaced. I've got access to the shutoff valve in the street, but that valve leaks a bit, too. The water doesn't flow with the street-side valve turned off, but there are a steady flow of drips (maybe a drip per second?).

What's the correct method to sweat on a new valve when the joint might still have a bit of water seeping through it? I've seen a couple videos on YouTube suggesting stuffing a piece of bread up the pipe, but the little voice in my head is saying "ummm...yeah, don't do that here."

My plumbing is all copper, and I would like to keep it that way. I'm pretty comfortable sweating joints on nice, dry, clean pipe.


  • 1
    get a long drinking straw and suck water out of the pipe
    – jsotola
    Jun 2, 2021 at 17:03
  • 1
    @jsotola long piece of tubing better than a straw - push it all the way out to the street valve. At the rate of 1 drop/sec it should allow hours of time.
    – user128019
    Jun 2, 2021 at 17:49
  • @stretch I was thinking about tubing also ... I suggested drinking straw, because most people would understand what I was talking about without needing an explanation
    – jsotola
    Jun 2, 2021 at 18:30
  • 1
    Why not use a compression fitting in this situation?
    – jay613
    Jun 2, 2021 at 18:34
  • I didn't consider a compression fitting! But now I'm curious why all the other methods for mitigating the leaking water to sweat on a fitting are proposed? Why not use a compression in any case like mine, and avoid sweating a fitting? Cost? Jun 3, 2021 at 2:10

2 Answers 2


You have to stop the water or when sweating it will have pin hole leaks.

The advice for bread is good if no pressure cheap white bread no crust I do this in horizontal runs all the time the bread turns to mush when there is running water.

Bread will not stop a pressurized leak. I use dry ice. Many grocery stores carry it but you have to ask, pack the dry ice around the pipe back a foot if you can and it will create a freeze plug allowing you to sweat the new valve in.

Then have fun with the dry ice put it in a bowl of water and watch it create “smoke” my kids loved this when I brought some home after doing a job.

The smoke is just carbon dioxide the same thing that makes fizz in soft drinks it’s not toxic but if in an enclosed space it could displace the oxygen, just be aware if working in a small closet to keep the door open.

The ice plug works great and is way cheaper than renting a machine to freeze the pipe I know plumbers that use both methods.


I use one of two methods, a shop vac running with a small tube placed through the opened new valve that has been cleaned and the tubing is also cleaned and fluxed. I then place the valve in place and sweat it. after it has cooled a bit I place the tube for the outlet in place and sweat it in place. If this does not work or the flow is a bit faster I get a compression valve, open it, put it in place, and tighten it, then close it and place the outlet piece of tubing in place and tighten it in place. Clean up the water and I am finished.

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