PVC Flexible Coupling Under Shower

[orangesoda123]

Hello Everyone!

Question about some plumbing work I'm about to do. I need to move the drain for a new shower install (installing in a basement, the drain is in an opening in concrete). I'm going to cut the current p-trap out to the main drain line that runs under the concrete floor and replace it with new fittings to get the drain where I need it to be.

My question is: Is there anything wrong or against code that would prevent me from using a flexible coupling from the main drain line to the new fittings/p-trap? I won't have enough exposed pipe left after removing the old stuff so I'm hoping to use a flexible coupling in case I goof something up after the fact. If I use rigid fittings and mess up, I won't have enough exposed pipe to try again without busting up concrete.

Any thoughts?


Thanks!

 

[wwhitney]

Maybe a picture of the critical area would help explain your concern?

A 2" plastic hub has a depth of 3/4", so you'd need 3/4"+ of clean sound pipe to glue on your new work. While an underground rubber coupling is 4" long, so you'd ideally have 2" of exposed pipe for that, although 1-1/2" would probably be fine.

Cheers, Wayne

 

[Sponsor]

 

[Reach4]

I doubt that is allowed. If I were inclined to use Spaflex, I would know that it is not allowed for this.

This video looks useful to me if using a pre-made shower base over concrete:

 

[orangesoda123]

I'll try to go snap a photo. I do have enough exposed for a 4inch rubber coupling. Just wasn't sure if that was legal or not.

 

[Reach4]

I'll try to go snap a photo. I do have enough exposed for a 4inch rubber coupling.

Flexible couplings are not that flexible to where you can use them for significant offsets. https://www.fernco.com/products/flexible-couplings/stock-couplings

 

[wwhitney]

I believe the OP's interest in a flexible coupling is only that it is reversible. The concern with using a glue coupling as I understand it is that if something goes wrong and he needs to cut it off, he may not have enough pipe stub left to try again.

Although if there's a 2" length of pipe stub available for a rubber coupling, seems like that would allow at least two glue joint attempts, which should be plenty.

Cheers, Wayne

 

[orangesoda123]

I believe the OP's interest in a flexible coupling is only that it is reversible. The concern with using a glue coupling as I understand it is that if something goes wrong and he needs to cut it off, he may not have enough pipe stub left to try again.

Although if there's a 2" length of pipe stub available for a rubber coupling, seems like that would allow at least two glue joint attempts, which should be plenty.

Cheers, Wayne

Correct. Definitely not to make it flexible. Just to give me another chance if I goof without too much trouble.


I attached an image. The star is where I will be moving the drain too. I think I'd still like to go down the road of using a flex coupling, but now after taking that photo I have a little more to play with than I thought.

 

[wwhitney]

So a rubber coupling is allowed, but I think most would consider a solvent weld connection to be more durable and a better choice.

One option is to make up all the new pieces and solvent weld them together, using a rubber coupling as your temporary dry-fit connection. Then once you've confirmed everything is in the right place, and you've successfully done those 3 solvent weld connections, looks like you'd have room to replace the rubber coupling with a solvent weld coupling.

Or you could just leave the rubber coupling, it is allowed.

Cheers, Wayne

 

[orangesoda123]

So a rubber coupling is allowed, but I think most would consider a solvent weld connection to be more durable and a better choice.

One option is to make up all the new pieces and solvent weld them together, using a rubber coupling as your temporary dry-fit connection. Then once you've confirmed everything is in the right place, and you've successfully done those 3 solvent weld connections, looks like you'd have room to replace the rubber coupling with a solvent weld coupling.

Or you could just leave the rubber coupling, it is allowed.

Cheers, Wayne

Thats a good idea. After I get everything sorted I can decide if I want to keep the coupling or weld at that point.

Thanks for the help and advice!!

 

[wwhitney]

BTW, the underground rubber coupling I have on hand has no internal stop, while a standard solvent weld coupling has a stop. So I think that would be an 1/8" difference if you end up switching, which you could accommodate in a number ways: cut your new pipe 1/8" shorter when you swap couplings, get a repair PVC coupling without a stop (then you need to mark each pipe to ensure the repair coupling is centered over the joint), etc.

Cheers, Wayne

 

[Terry]

Like Wayne, I would glue up a new coupling and p-trap for that.
Or use a coupling like this.

 

[wwhitney]

I've used couplings like that below grade in the past, but I found out this year that they are not rated for underground use. Of course, if you don't bury the rubber coupling in soil, maybe it's not underground. : - ) That one has a 1/8" stop, so it would make it easy to swap out with a solvent coupling.

Cheers, Wayne

 

[Jeff H Young]

never heard that a cast iron to plastic or pl to pl cant be used underground . but never looked into it.
I glue up fittings like that frequently you gotta kinda guesstimate with some dry fitting . then work fast glue it up and check your measurements if they are off you gotta quickly pull apart and cut or put longer piece . can't get it perfect first time every time but that's my low tech way of getting it done.

 

[wwhitney]

never heard that a cast iron to plastic or pl to pl cant be used underground . but never looked into it.

Yeah, I was surprised to learn that.

If you look at https://www.fernco.com/plumbing/shielded-couplings/proflex-couplings for example, the top paragraph says "for above-ground applications." And the approval listed is ASTM C1460, which is titled "Standard Specification for Shielded Transition Couplings for Use with Dissimilar DWV Pipe and Fittings Above Ground"

In contrast, https://www.fernco.com/products/flexible-couplings/stock-couplings says the unshielded rubber couplings are listed to ASTM C1173, which is titled "Standard Specification for Flexible Transition Couplings for Underground Piping Systems". If you want a shielded underground coupling, there's https://www.fernco.com/plumbing/shielded-couplings/strong-back-rc-couplings which are still 4" long.

Cheers, Wayne