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Thread: PVC into cast iron

  1. #1

    Default PVC into cast iron

    I am replumbing a bath and was told by my local plumber the you are not supposed to thread PVC into cast iron. The 4" stack has a 1 1/2" threaded hole where the old galvanized sink drain was joined and a previous plumber unscrewed the galvanized and threaded PVC into it. The threads look like they match, and it has been in place for 10 years and is not leaking.

    If this is not proper, what is the proper way to transition this?

  2. #2
    Plumber plumber1's Avatar
    Join Date
    Aug 2005


    Some fellas like to screw pvc to cast iron or galvanized.

    Personally I like to connect them with no-hub bands. I've seen the pvc come loose and I blamed it on hot water. Steel and pvc expand and contract at different rates.

  3. #3
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default pvc

    If the cast iron has a proper 1 1/2" thread, not a hole drilled and tapped, then there is nothing wrong with screwing the PVC into it.

  4. #4

    Default hole

    It does have a proper 1.5" thread. I believe he wanted to replace those drains to pad the bill. I can see replacing the lead closet bend on the first floor and the lower half of the stack going to the basement, but not all of the drains on the second floor too.

    BTW, it is a remodel and the walls are gutted to the studs.

  5. #5
    Plumber Cass's Avatar
    Join Date
    Nov 2005


    If everything is open and the drains are galvanized I would recomend their replacement also.

    My recomendation would not be so I could "pad" the bill.

    It only makes sense based on all the clogged/rusted out galvanized lines I have replaced over the years and it's only a matter of time B4 they will need to be replaced.


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