Can flexible coupling be installed on a toilet drain 3" ABS pipe?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Marius, May 11, 2021.

  1. Marius

    Marius New Member

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    May 11, 2021
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    Toronto
    I'm doing a bathroom reno on second floor, and in the process, I'm replacing the bathtub with a shower. The current bathtub drain 1 1/2" ABS it connects with the 3" ABS drain coming from toilet using a 3" wye ABS. I have to cut the wye and install a new one, this time on opposite direction, with the 1 1/2" filliped on the other side, where would merge with the new shower drain.
    The problem I have, the 3" drain pipe is fixed, and doesn't allow movement to install a regular, fixed coupling.
    It seems I have only two options:
    1. To use a 3" flexible coupling (Fernco) to connect the new wye hub to the main drain
    2. To replace the entire drain, including toilet flange and approx 5ft of new 3" pipe (and cutting more subfloor). This way the new wye can be glued to the main drain.
    I appreciate your thoughts on the two options and which one is recommended. Thank you!
     

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  2. Reach4

    Reach4 Well-Known Member

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    Use a shielded (metal band around the rubber) coupling.
     
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  4. Marius

    Marius New Member

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    Thank you for your response! I also thought about the shielded coupling (I think also called no-hub coupling), however, looking at some pictures, it seems the shielded version has a stopper in the middle, on the inside of the rubber. This stopper would prevent the rubber sliding back and forth, on the pipe, effectively having the same problem I had with the regular coupling (that gets glued).
     
  5. Reach4

    Reach4 Well-Known Member

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    That does not prevent you from sliding the whole rubber onto one of the pipes. Sliding on plastic is easier than sliding on metal. Sliding takes some work.

    Dish detergent is often used as a lube.

    While it is easiest if you can slide the shield farther on out of the way, it is also possible to remove the shield, and put it on around the rubber once the rubber part is in place.

    I did not mean to suggest option 1 is better than option 2. I was just saying that if you use non-glued connections the couplings should have the shield.
     
  6. Mr tee

    Mr tee In the Trades

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    Montana
    You can fold back the rubber then snap it back when the fitting is in place. The metal shield can either be slid up the pipe then slid back over the rubber or, if necessary, opened up then reassembled over the rubber.
     
  7. Marius

    Marius New Member

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    Thank you everyone for your quick replies!!

    Based on your responses, it seems that shielded coupling facilitates sliding, so I would definitely use this one, as clearly provides better support and prevents sagging.

    Any thoughts if option #1 merits the extra effort? Clearly it requires more effort, cutting the subfloor and rebuilding the entire toilet drain, Is it really worth it, all that extra effort, or the shielded coupling would work, long term, as good as the permanent glued coupling?
     
  8. Reach4

    Reach4 Well-Known Member

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    You may want to make a better plan view (bird's eye x-ray view) if you want opinions on that.
     
  9. Marius

    Marius New Member

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    Thank you Reach4 for clarifications, and pointing out for the dish detergent!

    Instead using dish detergent as a lube, I was also wondering if I could use a thin layer of Pipe Joint Compound (see pic). Beside making easier to slide, I'm wondering if the pipe dope would provide a better sealing between the rubber and ABS pipe.

    To rephrase my question, would the pipe dope do any damage to the flexible coupling?
     

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  10. Reach4

    Reach4 Well-Known Member

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    While I doubt it would do damage, I doubt it would be as slippery. I understand that bottle you posted the image indicates it has PTFE. If you have both, as a test I would put on some nitrile gloves, and slide finger against thumb with each as a lube. I am not a pro.
     
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  11. wwhitney

    wwhitney Well-Known Member

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    To clarify, shielded couplings and no hubs are slightly different. No hubs use a thinner corrugated shield and are only for connecting cast iron to cast iron. Shielded couplings have a thicker uncorrugated shield, and are available for a variety of different pie combinations. Fernco and Misson are the primary makes of shielded couplings.

    Cheers, Wayne
     
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  12. Marius

    Marius New Member

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    Thank you for pointing out the difference!
    I thought they're the same, but clearly they're not. In my case, the shielded coupling looks a better candidate.
     
  13. Marius

    Marius New Member

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    Please refer to the new picture, as I've tried to highlight the layout for option #1.
     

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  14. wwhitney

    wwhitney Well-Known Member

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    Shower drains are typically 2".

    I assume the riser on the right of your photo is for the lavatory(s)? That would be wet venting the shower and WC.

    I don't see what the blue option gets you. The combined WC/shower/lav drain continues somewhere, so you'd still be working between fixed ends.

    Just cut out the wye and install a new wye in the orientation you want using two shielded couplings.

    Cheers, Wayne
     
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  15. Marius

    Marius New Member

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    Thank you, that's a good point! My house is about 15 years old, and back then Builders used 1 1/2" for shower and tubs. Now that I'm redoing the shower drain entirely, I would get the 3 x 3 x 2 Wye hub, and use 2" ABS pipe all the way to the shower drain (p-trap etc). This would align more with the newer code.

    As for the blue option (option #1), as I work my way from the Wye hub towards the toilet, I should be able to glue all the fittings, all the way to the toilet flange (hence, I would always have a non-fix end). But there is considerable effort to cut subfloor and rebuild the toilet flange.

    Yes, using the shielded coupling seems the most efficient solution (and easiest), but wanted to get a second opinion, from someone that has more experience with this type of drain problem.
     
  16. Reach4

    Reach4 Well-Known Member

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    We are mostly not familiar with Ontario plumbing code. That code does not appear to give free access. So some things we know differ from US codes, but I don't know if 1.5 is still OK for a new shower. US codes generally call for the 2-inch now.
     
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  17. wwhitney

    wwhitney Well-Known Member

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    I don't understand this comment, based on the way the tub wye is oriented, the WC is downstream of the tub, so you wouldn't always have a free end, there would be the downstream fixed end to connect to.

    Cheers, Wayne
     
  18. Michael Young

    Michael Young In the Trades

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    Just open the floor and do it the right way. The fernco IS NOT A LEGAL FITTING. And your stated purpose for wanting to use one is so you can cheat a little bit to make things work. That is a really bad decision. Do it 100% right, DO put a water test on it. And yes - go ahead and call in a homeowner permit and get it inspected. If you get it wrong and it leaks later - how much shit are you going to have to tear out to fix it. DO IT RIGHT 100% OF TE TIME. You know cheating with that fernco is a bad idea. You have the skill to do this work and you're going to cheap out over a freakin’ sheet of plywood!! are you nuts!

    - Mike
    https://homeservicestriad.com
     
  19. Mr tee

    Mr tee In the Trades

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    If you use a shielded coupling you do not slide it, you fold one side back. The rubber is thinner than the unshielded.
     
  20. Reach4

    Reach4 Well-Known Member

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    Then I was doing it wrong. I think you would have to do some sliding, but apparently not as much as I did. I think "slide" implies something easier than it is.

    Sliding over the galvanized was tedious, and involved prying with a screwdriver.
     
  21. Tuttles Revenge

    Tuttles Revenge In the Trades

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    Oct 15, 2014
    You could slide a Shielded coupling/No hub band back like a repair coupling... but its a lot harder than just folding one side back over itself on the pipe. Folding back couplings is something every plumber does time and time again..

    Pipe Dope is a terrible idea for a lube as its messy and extremely viscous.. meaning its a much larger particle than a soap.. and it will stay liquid for a LONG time.. its just a terrible idea.
     

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