Brass P-Trap to Cast Iron DWV

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by jlsddmar, Jun 28, 2010.

  1. jlsddmar

    jlsddmar New Member

    Messages:
    13
    Location:
    Watertown, MA
    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. SewerRatz

    SewerRatz Illinois Licensed Plumber

    Messages:
    1,705
    Location:
    Chicago, IL
    please post some pics it will help us see what you are trying to do.[​IMG]
  3. jlsddmar

    jlsddmar New Member

    Messages:
    13
    Location:
    Watertown, MA
    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. SewerRatz

    SewerRatz Illinois Licensed Plumber

    Messages:
    1,705
    Location:
    Chicago, IL
    Thats a non-issue when it comes to drainage. Just be sure to use 17 guage p-traps.
  5. jlsddmar

    jlsddmar New Member

    Messages:
    13
    Location:
    Watertown, MA
    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. shacko

    shacko Master Plumber-Gas Fitter

    Messages:
    561
    Location:
    Rosedale, Md
    I think this is what you need

    [​IMG]

    That comes with a chrome lock-nut it's 1 1/2 male by 1 1/4 compression
    Last edited: Jun 28, 2010
  7. jlsddmar

    jlsddmar New Member

    Messages:
    13
    Location:
    Watertown, MA
    Hi -

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

    -Derek
  8. MACPLUMB 777

    MACPLUMB 777 TROJAN WORLDWIDE SALES RP

    Messages:
    679
    Location:
    Houston, Texas, United States
    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: Jun 28, 2010
  9. jlsddmar

    jlsddmar New Member

    Messages:
    13
    Location:
    Watertown, MA
    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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