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Thread: Connectent 2 inch PVC to copper for drain

  1. #1

    Question Connectent 2 inch PVC to copper for drain

    After suffering 3 different leaks on my 2 inch copper drain pipes, I decided to replace it with PVC. Each leak was at a joint, and I patch it last year, but took the dive and removed my downstairs ceiling for access.

    My hope is that I can replace everything up to the 4 inch copper stack, but am not sure the best place to join PVC and copper. Can I somehow have the PVC enter the stack, or do I need to cut the pipe 6 inches from the stack and join there? I am concerned as I don't know how good the copper is up to the stack. The copper pipes are 2 inch pipes entering the stack.

    Along with that, when I replace the copper drain pipes up to my sinks, can I do the copper cut above the sink drain Tee and replace with PVC. I don't know if there are concerns with the PVC supporting the copper vents.

    This sounds like a job for a plumber, but I am a weekend warrior, and love to take this on. I have access from below, and from the fixtures.

    Thanks

  2. #2
    DIY Senior Member Marlin336's Avatar
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    I'd cut the copper about three inches before the stack and inspect it. If it looks like it's in good shape use a no hub clamp. They make special ones for copper to PVC connections, don't get a regular 2in no hub clamp as it won't fit.
    Failing that... I'm assuming since the stack is copper that your two inch is soldered into the stack? If that's the case I'd cut it a few inches short of the stack, unsolder it, and clean out the Y very well. Then I'd do one of two things. One option is to solder in a new short piece of copper. The downfall here is they'll make you buy 10ft of 2in DWV copper for probably around $100 and you'll only use six inches of it. Your other option is if you can find some sort of street male adapter that you can solder into the Y on the stack. Then use a female PVC adapter on that. For soldering two inch you'll need a MAPP torch, propane won't cut it. You might need an acytlyne (I never could spell that word) torch to unsolder that fitting depending on how much crud is on the inside of it, what kind of solder they used, etc.


    As for the vents you should be able to cut them and use a copper to PVC no hub clamp. The vents should be strapped to the framing and able to support themselves, if not the PVC is probably more rigid then DWV copper, especially worn DWV copper.
    Last edited by Marlin336; 09-15-2007 at 04:52 PM.

  3. #3
    Licensed Grump GrumpyPlumber's Avatar
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    I'd strongly advise against unsweating (unsoldering) anything directly connected to a fitting on your copper stack, especially if you're unfamiliar with soldering.
    Heating the stack fitting will definitely melt/loosen the 2" pipe, also compromising the soldered seams above and below on the stack itself.
    You're best option is the copper to PVC mission clamp.
    IF the fitting at the stack is in as bad a shape as the 2" line was, you might want to seriously look into getting a pro.
    "The biggest regrets we have in life are the chances we never took."

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    DIY Senior Member Marlin336's Avatar
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    What I've done in the past to protect other joints was to just wrap a wet rag around them. GrumpyPlumber is right though, if you're unfamiliar with soldering you probably don't want to go messing with something like that.

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    Commercial Plumber markts30's Avatar
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    I would go with the transition coupling as well...
    2" copper to 2" PVC are easy to use and have never leaked on me in the past...
    As far as the info about MIP/FIP connections...
    Quote Originally Posted by Marlin336
    Your other option is if you can find some sort of street male adapter that you can solder into the Y on the stack. Then use a female PVC adapter on that.
    Here you have to screw the plastic into the metal...(the other way will almost always leak and the plastic female fitting can and will break from expansion and contraction)...

  6. #6
    DIY Senior Member Marlin336's Avatar
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    Quote Originally Posted by markts30
    Here you have to screw the plastic into the metal...(the other way will almost always leak and the plastic female fitting can and will break from expansion and contraction)...
    So you would need a copper street female adapter. That's good to know. I haven't had a problem with it in the past but will try to use male plastic fittings in those situations from now on.

  7. #7
    Commercial Plumber markts30's Avatar
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    Because of the nature/design of the MIPs in DWV plastic fittings, we usually make a habit of using half of a threaded SCH80 nipple and a DWV coupling for this purpose...
    Most breaks with DWV MIPs occur where the plastic is thinnest at the end of the threads where the socket of the fitting joins...

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