When to switch from PVC to ABS?

[grahamW]

I've now located the waste line under my slab.

Above the concrete, all the plumbing waste/vent lines are ABS, while below ground they are green/white PVC. My plan is to wye into the 15" long section of 4" green PVC (photos below) using no-hub couplings for my new floor and laundry drains. I'll be using a single 3" pipe to serve both. A rough sketch of all this was previously posted and I'd still welcome feedback.

My question is: At what point should I switch from PVC to black ABS? Is there a reason that PVC is used below the slab?





NB: I found a chunk of unused, busted green PVC pipe which is marked in the photos. It must have been discarded when they did the install and then filled over. Annoyingly, it looks more functional in the photos than it is.

 

[Jadnashua]

The choice of ABS or PVC is mostly a regional thing...use the one more common to your area so you have a choice of suppliers and fittings. There is no reason to change unless you want to. Now, if you're preferential to black verses cream colored...that might make a difference!

 

[Sponsor]

 

[grahamW]

I figured that there must be a reason that it changes above and below the slab. Seems strange.

 

[Hackney plumbing]

The pvc looks like sch 30 weight. Sch 40 fittings will not fit it.......if thats the case. Goodluck!

 

[grahamW]

Hackney, thanks for that. I put my calipers on that broken bit of green pipe and its thickness is 0.179" (i.e. schedule 30). This just keeps on getting more and more fun. Will it really matter if I'm using no-hub connectors for the wye?

 

[hj]

Green PVC S&D pipe is usually used outdoors. The only ones who use it indoors are the plumbers who underbid the job and have to cut corners. Standard fittings do NOT fit it, unless you use adapter bushings. The O.D. of the pipe is the critical thing. The internal "bore" will be 4" to match sch. 40 pipe. The thin wall will cause the O.D. to be undersized.

 

[grahamW]

Green PVC S&D pipe is usually used outdoors. The only ones who use it indoors are the plumbers who underbid the job and have to cut corners. Standard fittings do NOT fit it, unless you use adapter bushings. The O.D. of the pipe is the critical thing. The internal "bore" will be 4" to match sch. 40 pipe. The thin wall will cause the O.D. to be undersized.

Thanks HJ. As I've said before, they cut every corner they could when they built this place. If you think the plumbing looks suspect, you should have seen some of the electrical. I do wonder how they managed to join the black sch40 ABS pipes (which they used above ground) to these sch30 pipes/fittings that are below ground. Any thoughts?

So, my next question is what can I do about it. I'd like to put a 4x4x3 wye into that 15" section of green pipe. My thinking is that I can get a sch30 wye and a section of sch30 pipe and use no-hub couplings, but then I'm left with a sch30 3" opening. You mention adapter bushings; is there a bushing I can use to adapt the O.D. of the 3" sch30 to 3" sch40?

 

[Jerome2877]

From the pics it looks like you have fittings on both sides, I would cut the pipe at the fittings and use them to couple on to as the od shoud be very close. Then use a 4x4x3 abs Y and continue on with abs.

 

[grahamW]

My other option is to get a pair of 3" I.D. bushings, some 4" sch40 pipe and splice in a sch40 4x4x3 wye directly. This will use 2 bushings instead of one and effectively reduces the I.D. of the main sewer line leaving the house which is something I'm less than thrilled about. The bushings will also create 2 snag points for waste and there are 4 toilets up stream.

 

[hj]

There are thin adapter bushings whick fit over the green pipe to make the o.d. fit sch. 40 fittings. You use PVC to ABS transition cement to connect them to the pipe.

 

[grahamW]

The fellow at the local plumbing shop suggested I use a 4" flexible coupling (apparently different than a no-hub coupling). The green pipe, he insists, is SDR-35 and is used by the developers/builders to save a little money. It is used for all the sewer lines and they add a bushing and switch to sch40 ABS when they drop the size to 3" inside the home. The 4" flex coupling seems to fit quite loosely around the sdr-35 pipe he sold me, but he insists that if I sinch it down, it will be fine and will pass inspection.

 

[Tom Sawyer]

You can buy thin wall adapters that will take SDR back to PVC dimensions

 

[Jadnashua]

Banded (nohub) connecters are required above ground, rubber sleeves are allowed underground. the reasoning is that underground, the ends will stay aligned because of proper backfill. Above ground, there's nothing to keep them from becoming offset, thus the requirement for the metal reinforcement band. You could glue the transition adapter onto the pvc which would bring the OD up to that of the schedule 40 stuff - this would provide a tighter connection.

 

[hj]

IF you "squeeze" a Fernco coupling to make it fit the SDR pipe, there is absolutely no assurance that it will "line up" with the sch. 40 you are connecting to.