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Thread: Connecting PVC bathroom sink drain to old cast iron drain T

  1. #1
    DIY Junior Member Brucedude's Avatar
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    Default Connecting PVC bathroom sink drain to old cast iron drain T

    Help from a pro please!
    I'm replacing a bathroom sink in an old house. The previous sink drain had been poorly installed--the tail piece from the sink had been "caulked" into the cast iron T in the wall. When I removed the old tail piece, I realized the cast iron T either never had threads, or they had long ago rusted away. I am left with a cast iron drain nipple that has a rusty round hole in it. So--is there any way to retrofit a fitting into this hole to create a tight, professional connection between the cast iron drain and the new PVC sink tail piece? Is there such a thing as re-tapping the threads?

    I'd just love to avoid having to tear out the wall and install new drain line if I can avoid it. Thanks for whatever anyone can offer!

    Bruce

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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    I would try to cut only the sanitary tee out and replace it. If successful, the hole in the wall would be fairly small and easy to repair.

  3. #3
    In the Trades Gary Swart's Avatar
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    The thread are still there, just filled with rust. Yes, they can be cleaned out and made useable. The right way to do this would be with a male pipe threader, but these are expensive to buy for a single use. A plumber could easily do it, but there would be at least a minimum service call charge. What you might try is to get a can of PB Blaster (a super good penetrating oil) and a galvanized nipple. Soak the rust with PB Blaster then get the nipple started on the threads. It might require some scraping or brushing some rust off of the first few threads so the nipple threads will bite. The use a pipe wrench to turn the nipple in and out, cleaning the threads, respraying with PB Blaster, and repeating, getting a little deeper each time. Just be certain you don't cross thread the nipple when starting. As I said, this is not a professionals way of chasing threads, but with some elbow grease and time, it should work. If not, you can still call for the plumber. BTW, WD-40 is not suitable for this, it is not a penetrating oil. Once the thread are cleaned, an adapter will screw into the tee.

  4. #4
    Forum Admin, Expert Plumber Terry's Avatar
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    A picture may help.
    What you may have is a galvanized pipe nipple. If that is the case, you can thread in a new one.

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