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Thread: How do I join 2.75 cast pipe to 3 inch PVC tee?

  1. #1
    DIY Junior Member remache74's Avatar
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    Default How do I join 2.75 cast pipe to 3 inch PVC tee?

    Hello I removed a rusted tee fitting from my sink drain and Im trying to replace it with a PVC TEE. My existing pipe is 2.75" ID and big box stores only sell 3" PVC tee? Any Ideas?

  2. #2
    DIY Senior Member dj2's Avatar
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    Get no hub couplings (cast iron to PVC). Big box stores may not have a good selection, go to plumbing supply places which sell to the public.

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    In the Trades Gary Swart's Avatar
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    Inside diameter doesn't mean anything here. Pipe size is measured from the outside. Cast iron can have different wall thicknesses, so you must use the actual measurement. You need a special banded coupler to go from the old cast iron to 3" PVC pipe. Then your 3" PVC tee will connect to that. By special, I mean one that will fit your cast iron on one end and 3" PVC on the other. You won't find it at a Big Box store. You need to go to a real plumbing supply house...one where pros buy their materials.

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    DIY Junior Member remache74's Avatar
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    Okay I guess pvc and pipe are measured differently. My pipe is approx 3.25 OD and the pvc is 3.5 OD. So I will try to find a no hub reducer that will work for those numbers. Thanks for the help.

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    Forum Admin, Expert Plumber Terry's Avatar
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    Or you can pick up a copper by cast iron Mission coupling.

    Normally pipes are ID dimension. However the very old cast iron was sized more like copper pipe on the outside.


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    Moderator & Master Plumber hj's Avatar
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    It would be an unusual sink drain if it were connected to a 3" pipe.
    Licensed residential and commercial plumber

  7. #7
    DIY Junior Member remache74's Avatar
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    The tee is 3x3x2...That is the sink drain taps off the tee fitting with approx 2 inch pipe....The tee then goes up to vent and down to drain.

  8. #8
    Forum Admin, Expert Plumber Terry's Avatar
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    How about a photo 800 pixels or less?

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    DIY Junior Member remache74's Avatar
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    Okay so I called a plumbing store and the lady who answered the phone says I can use a 3 x 3 no hub coupling. Saying that even though the coupling is .25 inch larger than my pipe side that it will compress to fit the pipe once I tighten. Does that sound kosher? Sorry for being a pain with the questions Im an aircraft mechanic thats used to having everthing close tolerance.

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    Forum Admin, Expert Plumber Terry's Avatar
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    Does that sound kosher?
    No.

    But then she doesn't have to install it and make it work. So she doesn't like how the plumbers do it? My post above gives the right answer. I've been doing this in the field for forty years now.

  11. #11
    DIY Junior Member remache74's Avatar
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    Like you said copper to pvc no hub worked like a charm. It looks like my pipe was pre 1970 which was before the NPS (national pipe standard) was created. Explaining why my pipe was an odd OD. Thanks for the help.

  12. #12
    DIY Senior Member Hairyhosebib's Avatar
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    You might try going to Ace Hardware. They may carry Febco Fittings. They are an Indiana company that makes rubber fittings for odd sizes of pipes. They will tighten down with big hose clamps.

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