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Thread: 3" PVC stack into Cast iron cleanout

  1. #1

    Default 3" PVC stack into Cast iron cleanout

    I am adding a full bath into the 2nd floor of a Cape Cod. I have run a new 3" stack over to the existing cleanout in the floor, which is 4" cast iron. The cleanout has a 3 1/2" brass plug. Is there an adaptor available to bring me from 3" PVC to thread into a 3 1/2" cast iron fitting? What are my options?
    Thank you.

  2. #2
    Plumber Plumber2000's Avatar
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    Default

    Not that I'm aware of. 3-1/2" is an odd thread size. Sorry.
    Plumber for 20+years

  3. #3
    DIY Junior Member Phatbrain's Avatar
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    Arrow Pipe Sizes - now and then

    Greetings Snelson,


    I’m curious about your 3.5” pipe. A common mistake with pipe is trying to measure it with a tape measure. If your clean-out plug measures 3.5”, then what you have is a 3 inch pipe.

    It’s kinda like trying to find 2 inches or 4 inches on a 2 x 4 stud. A long time ago (in a land far – far a way…) when steel chemistry was crappy, the pipe walls were thicker. So, an I 1/2 pipe I.D. was 1.5”.

    As steels improved, they were able to make the wall thinner, but to keep the pipe “backwards compatible” with existing fittings, the pipe O.D. was kept the same as before.

    Pipe
    Size:

    1/2" =0.840" o.d.
    3/4" =1.050" o.d.
    1" =1.315" o.d.

    1 1/4" =1.660" o.d.
    1 1/2" =1.900" o.d.
    2" =2.375" o.d.

    2 1/2” =2.875" o.d.
    3" =3.500" o.d.
    4" =4.500" o.d

    5" =5.563" o.d.
    6" =6.625" o.d.
    8" =8.625" o.d.

    10" =10.750" o.d.
    12 =12.750" o.d


    Phat

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Default co

    About the only common bushing you will find is a 3 1/2" x 2" one. But the cleanout is not an approved sanitary fitting so you should not connect your drain to it, but should install a proper sanitary tee for the connection and be sure to retain, or provide a new, cleanout in that area.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Default

    [QUOTE=Phatbrain]Greetings Snelson,


    I’m curious about your 3.5” pipe. A common mistake with pipe is trying to measure it with a tape measure. If your clean-out plug measures 3.5”, then what you have is a 3 inch pipe.

    Cast iron cleanout tees and cleanout ferrules have a 3 1/2" plug tap. It goes back to the original specification that a cleanout opening had to be the size of the pipe, and a 3 1/2" tap was 4" o.d. and thus was adequate for a 4" pipe. It is still the same with cast iron, but plastic cleanout tees use a plug the same diameter as the pipe. 3 1/2" plugs are made in plastic also for use in cast iron fittings.

  6. #6
    DIY Junior Member Phatbrain's Avatar
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    Default

    Gotch - thanks HJ.

    The confusion on pipe / tubing sizes is one that I battle constantly.

    Phat

  7. #7

    Default

    Why can't I use the cleanout to connect an auxiliary DWV stack if I install a new cleanout into the new stack so that it can be used to reach both?

  8. #8
    Tradesman Plumber Kristi's Avatar
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    Default

    Macska, I think HJ explained that part already...?

  9. #9

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    Edited: HJ, plumguy and Kristi have kindly begun to address my question on another thread. No need to have two threads on the same issue.
    Last edited by macska; 09-17-2005 at 04:32 PM.

  10. #10

    Default ummmm

    anyways just to answer your question...they do make a 3 1/2" tp 3" reducing bushing =) it's available in both black, and galvanized.

  11. #11
    DIY Senior Member finnegan's Avatar
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    Default

    As Jimmie said, A plumbing supply store should carry the fitting you need. I just bought a black fitting and my store had it in stock. It is not a Home Depot item.

  12. #12
    Moderator & Master Plumber hj's Avatar
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    Phatbrain, I am curious how you inserted that quote and posted the reply using my "account".

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