when connecting pvc drain pipes to iron main, thread 101 please


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Old 06-16-18, 02:25 PM
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when connecting pvc drain pipes to iron main, thread 101 please

Okay, this seems to be a passinate subject in some places and im not trying to offend,
I just want to know the best way to do this and if i ask 10 plumbers seems each is a little or lot different in their replies but get angry if i ask, explain why you do it that way.

100 plus yo fixer upper upstairs bathroom someone started repairs 20 years ago and abandoned it.

I have a 1.5 threaded hole in a large main iron drain,
I desire to connect a new pvc pipe drain to it, that goes to the sink and tub,

Ive been told use a male threaded fitting screwed into the iron pipe and cement my pvc to it,
I have been told use Teflon tape with and without dope or dope only,

Then another way is use a galvanized nipple screwed into that iron pipe, then use a shielded rubber sleeve to connect the pvc pipe to that, and again some say tape some say dope some say both on the threads,

Then still others say use some rubber insert in the hole and just push the pipe in,

So which way am i best off with and why is it best and the others not,

Many thanks
b
 
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Old 06-16-18, 03:52 PM
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A lot depends on the condition of the pipe in the wall. If the threads of the female fitting are in good condition then you can screw PVC right into it. If the female fitting is rusted you may have better luck getting a water tight seal by screwing in a male steel fitting since you can tighten down harder.
 
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Old 06-16-18, 07:34 PM
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So just as i thought it depends,

The threads in the iron pipe happen to be super nice almost like new,
I would rather use pvc screwed into that, so now what do i put on the pvc threads?
 
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Old 06-16-18, 08:53 PM
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Use 3 or 4 wraps of teflon tape. 1" is a bit under-sized for a sink & tub, but if that's all you've got, it'll probably work.

If you have trouble with the PVC tie-in, it wouldn't be that difficult to cut it and replace it with a galvanized nipple. I would cut the thread off of one side of the nipple and couple directly onto pipe rather than coupling onto threads.
 
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Old 06-16-18, 11:50 PM
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Steve,

Im not so much having trouble as just wanting opinions and options, and tech info,

Not to sound pompous but i tend to be mechanical inclined,
But im also very OCD you should see the old vette im restoring, lol,

I liked the idea of just screwing that pvc adaptor into that iron drain then cementing the pvc pipe into that but then im told do it the nipple with shielded rubber connector way,

My mind wants details and pros and cons of each, yes, i like to learn,

1.5 is the size of the old drain pipe that was there and the hole in that big iron pipe is 1.5 i thought i read that was okay for bathrooms, so i felt locked in to 1.5
Even if i used 2 inch the 1.5 hole in the iron pipe would be a restriction so to speak,

The reason im not so keen on the metal pipe nipple way is the old pipe tore apart at the threaded part at that iron pipe it took about an hour of careful dremel and chisel work to get the old rusty threads out, but the iron pipes hole threads are super nice,
I dont want to deal with that nipple rusting but it would likely outlast me,

So you see im flippy on which way is best for me to do it.
 
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Old 06-17-18, 10:39 AM
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Any of the ways you pointed out will work.

I would go with the same advice. A PVC male threaded adapter with some dope would be the easiest. I like pipe dope since it will fill any voids and you don't have to be as precise with the number of wraps.

If you're happier going with a galvanized nipple and shielded coupler, that's fine too. A galvanized nipple will get you 30-50 years, no problem. Of course, PVC will be pretty much forever.

Chances are your cast iron stack is going to rust out before either fails.
 
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Old 06-17-18, 12:25 PM
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If you are OCD... the female threads can be cleaned up with a tap. With clean threads a male PVC will easily screw in and seal. The drawback is that a 1 1/2" NPT tap is rather expensive.
 
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Old 06-18-18, 02:00 AM
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Again thanks all,

The female threads in the iron stand pipe are in really great shape surprised me,
Cleaned up super
The male pvc screws right in no issues...
 
 

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