Belly in a 4" Drain Line

[MP-123]

Morning all,

I am renovating my bathroom and when I pulled the toilet, I noticed water in the bottom of the flange. Long story short, I rented a camera and found that the 4" branch that services the bathroom (toilet, shower and wet vent lav) were slopped the wrong way and that water was sitting in over 1/2 the pipe. Make sense why were would smell sewer gases every now and again. I dug up the concrete to correct the slope and found that the 4" line the bathroom connects to (about 6 feet away) has a belly in it and is also holding water (although not as bad). Now to my questions:

1. I ripped up the concrete about 4' on each side of the center of the belly. My plan is to just pull up the pipe to create the slope. I know I can cut out the pipe sections but I only need to pull it up about 3/4'. Also, based on how the pipe was laid, I actually can't get the proper 1/8" slope but can get it close to 1/8" over a 4' section. Know it's not idea but it way better than it was. The question is how much force can I apply to a 4" pipe with a wye in the middle before putting too much stress. I wrapped a wire around the wye and with a crowbar was able to forcibly pull it up to the needed slope. How strong is PVC?

2. There is plastic under the concrete (a lot thinner than I would have liked) and was wondering if anyone had any tips for repairing the plastic I tore out around the trenching.

Thanks in advance for all the help. Love the forum!

 

[CountryBumkin]

Pictures are nice. We like pictures.
Is this "belly" just a dip in the pipe at the center, or do you need to raise everything one end to maintain the slope (i.e. the closet flange and p-traps etc., connected)?
PVC is tough stuff. I doubt you will hurt it lifting it 3/4", but without seeing what you got, it's hard to provide advice. If both ends of the PVC pipe are fixed (still under the slab) and you just want to raise middle, the problem is that the pipe needs to "compress" or one end needs to shift. If the length of pipe you have exposed is long enough I don't think it would be a problem (3/4" is not that much). IMO.
On fixing the plastic tear, you could try the "house wrap" type tape. If necessary you could slide some new plastic under the piping then seal the edges with the tape.

 

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[MP-123]

Sorry for not including a picture. Here you go.

Yes, the belly is in the middle. I cannot get a perfect slope, but can get a little better than level by pulling up the middle section (with the wye). I had to use decent force to lift and am curious if the stress could damage the PVC over time? The only way to get a perfect slope would be to dig up the whole line which would be pain in the butt. After I pulled up the belly, I did use a camera and saw the water traveling down the line and it's not pooling too badly. After a few mins, the drain is clear of water.

 

[CountryBumkin]

Sounds like you got it fixed. Good work.