How do I Extend Existing Waste Pipe In Order to Attach Toilet Flange

[Laxmidi]

I'm renovating a bathroom and I need to extend the existing 4 in. (steel or cast? I'm not sure which) waste pipe in order to attach a PVC toilet flange. The lip of the existing pipe will be about 4-6 in. short of the finished floor height.

Should I use a compression donut and reduce the pipe size from 4 in. to 3 in.? Would this result in more clogs?

Or should I use a 4 in. x 4 in. Proflex shielded coupling? It looks like a neoprene sleeve with two clamps around it. The pipe lip is slightly jagged-- it's not cut perfectly square. Would it leak if it's not square? I would have to remove wood in order to get an angle grinder on top of the pipe, so that might be an issue.



Please note the jagged end of the pipe.

It sticks out of the concrete a little under 3 in.
Any suggestions? Thank you.

 

[Cacher_Chick]

If the riser is long enough, the shielded coupling should work fine.

 

[Sponsor]

 

[Reach4]

Or should I use a 4 in. x 4 in. Proflex shielded coupling? It looks like a neoprene sleeve with two clamps around it. The pipe lip is slightly jagged-- it's not cut perfectly square. Would it leak if it's not square?

I think you are describing a vertical cast iron pipe, and I expect the jags that you describe do not increase the OD. So a shielded coupler as you described should work fine. https://www.fernco.com/plumbing/shielded-couplings/proflex-couplings ... looks like Proflex # 3000-44 (4" CI, to 4" PL.) or Mission CP-44 would be what you want. "PL" means plastic i.e., PVC or ABS.

I would have to remove wood in order to get an angle grinder on top of the pipe, so that might be an issue.

Remember you will have to access the screws to tighten the coupler. 5 ft-lb is the normal torque. You don't need a torque wrench. Just don't see 60 inch-pounds and confuse that with foot-lbs.

I am not a plumber.

 

[Laxmidi]

@Reach4 Thank you for the message. I added a pic of the existing waste pipe

 

[Terry]

A shielded coupling works fine. Most trapways on toilets are 2".
3" works fine, but in your case, 4" may be even easier to install. Flanges come in many flavors.
A 4" hub flange or a 4x3 hub flange.

 

[Cacher_Chick]

Your photo makes it pretty hard to see how much pipe is sticking up. A banded/shielded coupler needs about 1-1/2" of pipe to clamp onto the outside diameter.

 

[Laxmidi]

A shielded coupling works fine. Most trapways on toilets are 2".
3" works fine, but in your case, 4" may be even easier to install. Flanges come in many flavors.
A 4" hub flange or a 4x3 hub flange.

Terry, thank you very much for the advice... When using the shielded coupling, does it matter if the end of the existing pipe is jagged? Do I need to prepare the end of the pipe somehow or will the coupling shielded coupling work on a rough end? Thank you.

 

[Laxmidi]

If the riser is long enough, the shielded coupling should work fine.

cacher_chick Thank you very much for the message...I added another pic.

 

[Terry]

Terry, thank you very much for the advice... When using the shielded coupling, does it matter if the end of the existing pipe is jagged? Do I need to prepare the end of the pipe somehow or will the coupling shielded coupling work on a rough end? Thank you.

Those cuts tend to be aways a bit jagged.

 

[Reach4]

That little notch will not hurt.

I would use some plumber's grease or silicone grease, but that is overkill. I am not a pro, and I am prone to overkill.

That is the cleanest looking old cast iron soil pipe picture that I have seen.

 

[Laxmidi]

That little notch will not hurt.

I would use some plumber's grease or silicone grease, but that is overkill. I am not a pro, and I am prone to overkill.

That is the cleanest looking old cast iron soil pipe picture that I have seen.

Thanks @Reach4. I go for overkill, too. I cleaned the soil pipe!