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Thread: Brass P-Trap to Cast Iron DWV

  1. #1
    DIY Junior Member jlsddmar's Avatar
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    Default Brass P-Trap to Cast Iron DWV

    Hi Everyone -

    What is the correct way of joining brass to a cast iron stack? Does the connection from a sink P-trap (brass) to cast iron need to be dielectric? My condo is in a high-rise type building, so code states that a PVC trap isn't an option for me.

    Also, does cast iron dwv frequently have either 1 1/2 and 1 1/4 inlets? I had been looking at the Kohler K-8998 but need to check to see if the pipe's opening is larger than 1 1/4.

    Thanks,
    Derek

  2. #2
    Illinois Licensed Plumber SewerRatz's Avatar
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    please post some pics it will help us see what you are trying to do.

  3. #3
    DIY Junior Member jlsddmar's Avatar
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    Hi Ron -

    The wall's pretty much closed up now, so I don't think I'd be able to get anything to come out clearly. I think the installation is pretty standard though. It's a 4" CI stack that runs up through the 7 floors of an apartment-type building. The pipe has a female threaded inlet for the sink drain, which was temporarily capped with PVC when the old sink vanity came out.

    I want to install a chromed brass 1 1/4 P-trap to the cast iron, and know that copper 1/4 sweat to MIP adapters exist, but am I going to run into corrosion issues due to the different metals being in contact?

    Thanks for the help,
    Derek

  4. #4
    Illinois Licensed Plumber SewerRatz's Avatar
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    Thats a non-issue when it comes to drainage. Just be sure to use 17 guage p-traps.

  5. #5
    DIY Junior Member jlsddmar's Avatar
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    Sounds good, thanks for the help.

    Do they make the adapters I'm looking for in brass, or is copper the way to go?

  6. #6
    Master Plumber-Gas Fitter shacko's Avatar
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    I think this is what you need



    That comes with a chrome lock-nut it's 1 1/2 male by 1 1/4 compression
    Last edited by shacko; 06-28-2010 at 11:51 AM.

  7. #7
    DIY Junior Member jlsddmar's Avatar
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    Hi -

    Yeah, I think it's something like that. That's a slip fit though, right? My P-trap is brass.

    -Derek

  8. #8
    TROJAN WORLDWIDE SALES RP MACPLUMB 777's Avatar
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    Use a 1 1/2" x whatever galv nipple from ci drain out to your brass p-trap
    THIS HAS BEEN PLUMBING CODE IN CITY OF L. A.
    Last edited by MACPLUMB 777; 06-28-2010 at 12:34 PM.

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  9. #9
    DIY Junior Member jlsddmar's Avatar
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    Hi Jerry -

    How is the brass connected to the galvanized? The P-trap isn't threaded. I was anticipating screwing the threads into the CI and then sweating the P-trap on.

    Thanks,
    Derek

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