ABS Main Drain to PVC tie in

[Alex S]

Hi all,

New to Houston and their lack of stocking ABS anywhere for a reasonable price, so I am going to use PVC to tie in a new main floor bathroom.

For vent pipes etc I have no issue using Transition Cement (Green) to go new PVC to existing ABS, but when it comes to the main drain exiting the house that will be reburied in Concrete, I become a bit more critical of my lax ways.

From what I understand the only approved for underground tie ins between different plumbing components is a mechanical coupling (a no hub / shielded / standard flex coupling).

Being a main drain it would be easiest to do this, because you can't really splice into a main drain and find room to glue the splice in anyways.

My question is for anything else like that ...Is a mechanical coupling for PVC to ABS really the only approved method?

Forgive my ignorance, but I have done some tests myself (maybe I am a fool testing a fools methods...and I know this) and I would bet a good chunk of change that a mechanical flex coupling would fail before transition cement.

Am I crazy?

 

[Reach4]

From what I understand the only approved for underground tie ins between different plumbing components is a mechanical coupling (a no hub / shielded / standard flex coupling).

Being a main drain it would be easiest to do this, because you can't really splice into a main drain and find room to glue the splice in anyways.

How about a photo of the area you want to splice in? Underground, you can use shielded or non-shielded.

My question is for anything else like that ...Is a mechanical coupling for PVC to ABS really the only approved method?

Many places approve the use of the green transition cement for drains.


The spec for green transition cement is ASTM Standard D 3138 (D3138). The codes for Texas allow that. https://www.uth.edu/dotAsset/b34d2db7-2c6e-4761-9484-81b3a68b9d71.pdf (spec for The University of Texas Health Science Center at Houston construction) mentions D3138 in section 3.3.I.6. I infer from that that Houston does not have a special prohibition.

What I have a hard time picturing is where using the flex couplers is much harder. I am not a plumber.

 

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[Alex S]

How about a photo of the area you want to splice in? Underground, you can use shielded or non-shielded.


Many places approve the use of the green transition cement for drains. I don't know about Houston. What I have a hard time picturing is where using the flex couplers is much harder. I am not a plumber.

Thanks for the reply.

I should clarify your statement though as I am also not a plumber and I might have been misunderstood.

I dont think the flex couplers are harder to install at all. To the contrary, they seem not only easier but in fact the only way to reconnect after cutting a piece of the main drain off.

Imagine this drain underneath the house, you bust up the concrete around where you want to work on it. Dig out around the section you are going to tie into, and you hack off a 3ft section.

Now someone tells you, nevermind, reconnect that pipe up that you just hacked a 3 ft section out of.

You can't really use a coupler with cement... in my brain at least..due to the fact you need some flex in the pipe to make up the connection. How could you get the 3ft piece back on? Even if you cut the 3 ft piece back to accommodate the new length due to some plastic couplers you install on the main drain. The main drain isn't going to flex for you, so gluing the piece back in doesnt seem like it would work. Somehow you would need something to flex a bit to get it in the right place and then push it together to let the glue/cement do its thing.

The flex couplers or no hub or shielded, whatever, all have the same principle where you can put it on the existing main drain, slide the shield / clamps back. Then you can fold back the rubber coupler, slide your pipe in, and fold the rubber over the installed pipe piece, slide the clamps/shield back on, tighten, you are done.

Does that make sense? No idea how that would be done if the main drain had no give to it which i imagine it doesnt buried under a slab.

 

[Reach4]

I should clarify your statement though as I am also not a plumber and I might have been misunderstood.

I dont think the flex couplers are harder to install at all. To the contrary, they seem not only easier but in fact the only way to reconnect after cutting a piece of the main drain off.

I am not sure what you were asking then. What would you like the answer to be? (which is a classic CPA question). Then people could pass judgement as to whether that is wise and allowed.

If your question is "what is the best way ....?", then a photo tells the story best.

When working with flex couplers, hand dish soap is a good lube. Tighten the clamps to 5 ft-lb (60 inch-pounds), or a reasonable approximation. A nut driver or screwdriver makes it unlikely that you overtorque a lot, but a ratchet makes it easy to over-torque.

 

[Alex S]

I am not sure what you were asking then. What would you like the answer to be? (which is a classic CPA question). Then people could pass judgement as to whether that is wise and allowed.

If your question is "what is the best way ....?", then a photo tells the story best.

When working with flex couplers, hand dish soap is a good lube. Tighten the clamps to 5 ft-lb (60 inch-pounds), or a reasonable approximation. A nut driver or screwdriver makes it unlikely that you overtorque a lot, but a ratchet makes it easy to over-torque.

Thanks for the input Reach. Your info has been great.
Sorry I wasn't more clear ... I was just having a hard time understanding how on earth a mechanical coupler was "Stronger" in the eyes of some code than the Transition cement. I thought I would have been missing something and although my wife thinks I don't listen I do appreciate a second perspective.

Texas allows it, which is nice for my DIY shower vent reroute in the attic because the ABS to PVC green goop is clearly visible (I am expert can you not tell? haha). I just couldn't understand the reasoning behind someone/a governing body/a piece of code whoever says the rubber sleeve and some band clamps were a "better" solution.

I dont have a specific problem that I need answering nor am I fishing for a "tell me I'm right" .. I just wanted some perspective on the ABS to PVC coupling methods as I have never had an issue with the Transition cement, but I knew some codes say no deal to that.

I have a main drain made out of ABS and I will need to tie in a new half bath, but I am forced to use the mechanical coupling regardless, it just sort of sparked my interest in the debate (or lack there of).

Originally from Canada where you can readily buy ABS and PVC at Home Depot / etc ...came down here...no ABS....sat here scratching my head as to why, and if transition cement is approved in the code here that explains it missing at the Depot haha.

 

[Reach4]

Part of what I think you are saying is that you expect the tensile strength of a glued joint would be greater than the tensile strength of a flex coupling, shielded or not. You wonder why any authority would allow the flex couplings without also allowing the transition-cement joints. Maybe they think the flex couplings would be easier to inspect?

An advantage of the flex coupling IMO is the ability to rotate the joint to get angles on wyes and tees ideal.

 

[Alex S]

Part of what I think you are saying is that you expect the tensile strength of a glued joint would be greater than the tensile strength of a flex coupling, shielded or not. You wonder why any authority would allow the flex couplings without also allowing the transition-cement joints. Maybe they think the flex couplings would be easier to inspect?

An advantage of the flex coupling IMO is the ability to rotate the joint to get angles on wyes and tees ideal.

Actually your last point is something I never considered. That little bit of bend would be hugely helpful. Is there any harm in that? No I assume, but say I needed 3 degrees or so to get the fit up to match up, that flex coupling would still seal just fine I imagine. So long as the 3 degrees is taken from between the clamps haha.