No hub vs. flexible Fernco for under slab sewer PVC?

[MiloCraft]

I need to wye into a tight spot on an existing under slab 4" PVC sewer drain. The location is underground and regularly damp/wet. I plan to use a Fernco coupling but have not found reliable information as to the best solution:

1. Fernco Proflex 3005-44 with a stainless steel sleeve over a thinner neoprene gasket.
2. Fernco 1056-44 flexible coupling made with thicker flexible PVC.

I have heard the stainless steel shield on the no-hub adds strength against sheer stress, but I have also heard the thicker flexible PVC on the flexible coupling makes for a more reliable seal.

Another consideration in my case is the outer diameter of my PVC sewer pipe is 4.2"
The Fernco Proflex 3005-44 gasket has an inner diameter 4.44" while the Fernco flexible has an inner diameter of 4.5". Are both of these connections even suitable for my application? I called Fernco and they recommended I use the flexible coupling. I didn't find this answer reliable as Fernco actually makes a Proflex meant to connect 4" sched 40 PVC to 4" thinwall PVC (gasket ID 4.44" to gasket ID 4.16"). Interestingly, they do not make any thinwall to thinwall couplings. Fernco wasn't able to provide any explanation on this topic..

I would appreciate any clarification or what plumbers' usual practices in this case would typically be.

Thank you

 

[Reach4]

Fernco Proflex 3005-44 with a stainless steel sleeve over a thinner neoprene gasket.

https://www.fernco.com/plumbing/shielded-couplings/proflex-couplings says

Proflex connects cast iron, plastic, steel, copper and tubular, drain waste and vent systems for above-ground applications.
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I don't know why.

They have some more expensive shielded couplings. https://www.fernco.com/xl-couplings is a mix of shielded and unshielded. I have not used them.

 

[Sponsor]

 

[MiloCraft]

https://www.fernco.com/plumbing/shielded-couplings/proflex-couplings says

Proflex connects cast iron, plastic, steel, copper and tubular, drain waste and vent systems for above-ground applications.
​

I don't know why.

They have some more expensive shielded couplings. https://www.fernco.com/xl-couplings is a mix of shielded and unshielded. I have not used them.

I cannot believe I missed that - thank you for pointing it out.

I would have liked to use the XL line the fittings are too long. Looks like I will have to go with their classic 4.5" flexible coupling.

Thank you

 

[wwhitney]

If you want a shielded version of an underground coupling, the starting option is the RC 1000 line:

https://www.fernco.com/dimensional-drawings/1056-44rc

If your 4" underground drain is SDR35, then you can glue a bushing on the outside of the pipe to make it 4.5" in OD to match the couplings. First option is an SDR35 - Schedule 40 bushing. Eg NDS 2P42 (plenty of other manufacturers, that's just the first I found):

https://www.ndspro.com/PDFs/Tech-Sp...-and-Drain-Adapter-Bushing-2P41-2P42-2P43.pdf

Second option is just a bell end from an SDR35 bell end pipe, in my experience the bell end is 4.5" OD. I forget if cutting the hub off an SDR35 fitting would work; I think they are too thick, plus they often are not smooth on the outside but have embossed info.

Cheers, Wayne

 

[MiloCraft]

Thank you Wayne for both of those tips - exactly what I need.