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Thread: threading PVC fitting into cast iron stack

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    DIY Junior Member ksudar's Avatar
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    Default threading PVC fitting into cast iron stack

    Hello.. I'm redoing a bathroom and have to replace a section of 1-1/2" galvanized drain pipe, which runs horizontally before it meets the main cast iron stack. Now, I was able to remove all of the galvanized pipe and found a 1-1/2" PVC threaded male coupling that will thread into the cast iron hub. My question is whether this will work, and if so what type of sealant I should use on the threads? Thanks for the help-

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    DIY Junior Member jc60618's Avatar
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    I use teflon tape and Megalock pipe dope. I also would use a PVC schedule 80 male adapter instead of the regular one.

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    DIY Junior Member ksudar's Avatar
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    thanks for the help... I'll give the pipe dope a try and see if it holds.

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    Master Plumber-Gas Fitter shacko's Avatar
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    What you have will work, I only use pipe compound on them, make sure you clean the metal threads and don't cross- thread it.

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    DIY Senior Member asktom's Avatar
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    I would use a male adapter on a drain rather than a sch 80 nipple. The nipple reduces the ID of the pipe, creating a place for things to start to clog

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    DIY Junior Member ksudar's Avatar
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    Quote Originally Posted by asktom View Post
    I would use a male adapter on a drain rather than a sch 80 nipple. The nipple reduces the ID of the pipe, creating a place for things to start to clog
    This is what I used - I did look for the sch. 80 fitting but they only carried 1-1/4" and smaller. Luckily the cast iron threads were still in pretty good shape, even though the galvanized piece had rusted out. And I'm pretty sure the old pipe was sloping in the wrong direction too.

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    Irrigation Contractor Fireguy97's Avatar
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    The "Rules" of PVC, according to the manufacturers.
    (From another forum, courtesy of TreeMonkey)

    Apollo Company strongly recommends not using plastic piping with metallic ball valves, 4th paragraph down:
    http://www.apollovalves.com/_docs/CautionPage.pdf

    Spears (and more so, Lasco) strongly suggest that you only use sealant, not tape, on threaded PVC fittings. The Lasco link to follow goes in to great detail.
    http://www.spearsmfg.com/how_to/FG-3...06_English.pdf

    And finally, Lasco has all kinds of rules about using threaded PVC: Sch. 80 not to be mixed with sch 40, absolutely no tape, etc., with a lengthy explanation of the engineering principles behind it. http://www.lascofittings.com/support...dedPlastic.asp

    http://www.lascofittings.com/support...dedPlastic.asp

    http://www.lascofittings.com/support...e40threads.asp


    The Lasco site has several more links to info about threaded PVC such as this one:
    Why PVC Threaded Connections Fail:
    http://www.lascofittings.com/support...ctionsFail.asp

    Mick
    Last edited by Fireguy97; 07-23-2010 at 07:41 AM.

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