Connecting p-trap to old 1 1/2 inch steel pipe?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Chris in Redlands, Sep 6, 2021.

  1. Chris in Redlands

    Chris in Redlands Member

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    Total amateur question here, but I'm trying to figure out how best to stub out the drain pipe that will eventually connect to the p-trap so i can finish tiling, but I don't yet know what sort of p-trap i'll be installing. Might be a decorative exposed one or just a standard PVC one, depending on what we decide to do with the sink/vanity.

    Is there a standard way professionals deal with this? While removing the old (1956) pipe, the only thing that would break free when i turned it were the threads connecting the pipe to the main drain pipe, so I need something that can be screwed into that, and that is about 4 inches inside the wall. I would think there's a simple solution involving some sort of ABS adapter (saw many kinds at the big box) to screw into the drain pipe that lets you add anything you want from the escutcheon out at a later date.

    I only have three or four good threads to screw into due to old corrosion, so tips on how to ensure a leak-free junction there would be appreciated as well.

    Good for a laugh, this is an ongoing bathroom remodel that I first came here for help with back in April. I'm trying to beat my old record (6 months) on remodeling the master bath. ha!
     
  2. Reach4

    Reach4 Well-Known Member

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    Your description may not be as clear as you think it is.

    Your "about 4 inches inside the wall" sounds like you might be exaggerating.

    A pro would probably open the wall. I am not a pro.
     
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  4. Chris in Redlands

    Chris in Redlands Member

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    Thanks! I probably should have shared some pictures. here's the old pipe with the escutcheon attached. It's more like 3 3/4 inches, i guess. You can also see how much thread i have to work with, and the corrosion that this old dog suffered over the years.

    [​IMG]

    And here is the hole in the wall. I'm tiling around it for the moment, but if there's a reason to open the wall, i guess i could stop.

    [​IMG]

    I can't see any benefit to opening the wall, since it's the same threaded hole in there either way...curious to hear what i'd gain by opening it up.
     
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  5. Reach4

    Reach4 Well-Known Member

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    Last edited: Sep 6, 2021
  6. John Gayewski

    John Gayewski In the Trades

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    If you can't find a tap just use a good threaded piece of pipe (not the old one) and run it in and out a few times. Don't go over 3.5 rotations while cleaning it.

    Then take a piece of pvc. Glue a male adapter onto it. Thread it into the hole.
    Leave the opening in the tile large enough to get a trap adapter over the pipe and into the hole (1/4" to 3/16" all the way around the pipe).

    Eventually when your done you can tape and dope the threads of the male adapter and screw it into the threaded fitting until it seals. Then cut it to length and slip the trap adapter on. Use a deep escutcheon. For trim.
     
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  7. John Gayewski

    John Gayewski In the Trades

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    The also the join of buying a threaded sched. 80 nipple 6 to 8"long and using that
     
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  8. Jeff H Young

    Jeff H Young In the Trades

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    Hi Chris, I'm practically a Neighbor Jeff from Highland!
    I'd probably get a new 6 inch gal nipple put dope on threads and run it back and forth just like John said and change if necessary on finish. Note : don't go crazy tight on it till you set finish you might need to change nipples depending on trap
     
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  9. Reach4

    Reach4 Well-Known Member

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    Maybe a get a longer nipple to work the threads. That will make it easier to grab the pipe for torquing without messing up the other set of threads. So after working the nipple for a while, flip it around and try the new threads.

    Or cut longitudinal saw kerfs in one for better thread chasing.
     
  10. Chris in Redlands

    Chris in Redlands Member

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    Wow, thanks for all the good tips! I had planned on using a small flexible shaft tool with a burr on the end of it to knock down the corrosion beyond the three or four good remaining threads in the drain pipe. As you can probably imagine, the threaded hole into the drain pipe is so corroded that the ID of the corroded part is actually smaller than the still-intact threaded part from the expansion of the rust. I do like the idea of chasing the threads with a homemade "tap" made of a long nipple with saw kerfs! looks like a real tap that size runs more than $40. Would be good to have that for the next time i need it, if only there was going to be a next time.

    I had assumed that whatever p-trap i ended up with, i'd have ABS between the p-trap and the steel drain pipe in the final build. Should I use PVC instead? Seemed the adapters for this sort of project are mostly in black ABS at the big box store. Either way, sounds like a simple glue-up threaded adapter with a length of 1 1/2 inch ABS/PVC stub out to be cut to length later is the ticket. I'll leave the hole in the wall just small enough that a good-sized escutcheon will hide it, so i'll have as much opening to work with as possible.

    Will pipe dope damage ABS or PVC?

    Thanks again!
     
  11. Chris in Redlands

    Chris in Redlands Member

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    Highland! Just down the road!

    Would you recommend the final build be galvanized rather than plastic? I was leaning toward plastic assuming my odds of getting a reliable seal would be better with plastic than with metal and pipe dope.
     
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  12. wwhitney

    wwhitney Well-Known Member

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    Look for one labeled as compatible with plastic.

    If you wanted for some reason, you could use a 1-1/2" brass nipple instead of plastic plus male adapter. There are also brass trap adapters.

    Cheers, Wayne
     
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  13. Jeff H Young

    Jeff H Young In the Trades

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    It really varies Chris , if its just a cabinet its simple. but a pedestal sink often involves opening wall and repositioning waste, and fancier trim that you dont want to have to open . pipe dope type is available that is good for abs , pvc , and steel , gas. then youll be covered for any home project
     
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  14. John Gayewski

    John Gayewski In the Trades

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    Pipe dope doesn't damage pvc or abs
     
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  15. wwhitney

    wwhitney Well-Known Member

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    Interesting. I was under the impression that solvent/oil based pipe dopes are not to be used on plastic pipe. E.g. this vendor's description of Oatey Pro Dope says "Do not use on . . . plastic pipe."

    https://www.homedepot.com/p/Oatey-Pro-Dope-8-oz-Pipe-Joint-Compound-154202/100204007

    However, when I go to the manufacturer's web site and check the spec sheet, while it only lists metal materials under "Pro Dope can be used on," the spec sheet doesn't explicitly say "do not use on plastic pipe."

    https://www.oatey.com/products/hercules-pro-dope-1185446064

    Nonetheless, I'd be inclined to only use a pipe dope that lists ABS/PVC on the list of acceptable types of pipe, e.g. this dope from the same manufacturer:

    https://www.oatey.com/products/oatey-great-white-pipe-joint-compound-with-ptfe--275767012

    Cheers, Wayne
     
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  16. John Gayewski

    John Gayewski In the Trades

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    I tend to use dope that can be used for anything. Job specific dope seems like a silly thing that manufacturers of dope would want you to invest in. If it's not safe for every (or nearly every) application get rid of it. That's where I stand on dope.
     

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  17. Jeff H Young

    Jeff H Young In the Trades

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    me too with prefering one for everything , but ive got several other kinds too I can easily get by with a few. a homeowner for few projects even just one.
    oh dont forget marked potable water as well! We should all follow the specs even if we think it dosent matter , its really the right thing to do
     
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  18. DIYorBust

    DIYorBust Active Member

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    I'm going to us a sch 80 nipple for a similar project soon. However I think a galvi is probably best practice. The galvinize you took out probably goes to a cast iron tee or less likely a galvanized tee. The plastic has different thermal expansion rate than the metal and could theoretically leak, so there's an argument to make the transition is a visible spot rather than behind the wall. But probably you get away with it either way.

    On the dope, as a homeowner, I've found a tin of megaloc covers the vast majority of my dope needs. However for this task I would prefer Teflon tape as it will resist seizing better in my experience.
     
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  19. MACPLUMB

    MACPLUMB In the Trades

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    I Like the Teflon Tape covered by the Megaloc it seals all joints
     
  20. Chris in Redlands

    Chris in Redlands Member

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    I think I'll go with a "belt and suspenders" approach, teflon tape + some sort of dope. Interestingly, after pricing 1 1/2 galvanized pipe with at least 1 end threaded to make a homemade "tap" i discovered that it's actually less expensive to buy a tap on ebay. Picked one up today for $30 shipped.

    While I'm waiting for it to arrive, another stupid question comes to mind. What can I use to hold the thing? I'll be damned if i can find even a picture of the end you hold it with while using it. ha! I have socket sets in every size, including 1/2 and 3/4 drive...but i'm guessing i'm going to need a wrench specific to this large tap?
     
  21. MACPLUMB

    MACPLUMB In the Trades

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    NO JUST A PAIR OF 440 CHANNEL LOCKS
     
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