Sewer back up

[Shane]

I am trying to help sort out a sewer issue in a renovation project. The pictures show the general layout. Working left to right, (2) water closets/sinks enter the double wye which was later changed to the second picture to try and alleviate the problem. The next double wye picks up a shower and a tub and then everything exits to the right. The main line is 3" PVC and the longest run is approximately 15 ft with a slope of ~1//8"/ft which appears to meet the codes. The problem occurs at the beginning where the water backflows up the opposing line ~3 ft and then slowly drains down. Each fixture is vented. There are 12 fittings along the trunk due to the joist direction relative to the trunk line

Is it as simple as increasing the fall to 1/4"/ft? Are there frictional forces from each of the fittings that need to be accounted for some how? Any suggestions?

Thanks

 

[Jeff H Young]

run a camera or snake it. 1/8th inch should flow I never run 1/8th if I dont have to. not too much detail Has it plugged up one or twice in a year ? or its just a few days or imediate problem? Somebody drop something down a pipe 1 1/2' or 2 inch fitting inside there a lot can happen a litle cut off piece of wood dropped down a closet bend

 

[Sponsor]

 

[Reach4]

Where is blockage?

If the center of the double wye at B was extended outside, you could run a snake in there.

 

[Sylvan]

Too many 90's and not enough pitch

 

[John Gayewski]

It looks like the fitting at N could be a regular 90 instead of a long sweep. Is that the case?

 

[Shane]

Here's a little more information.

The blockage is occurring around "D". I agree, it is a pretty flat line. Here's another picture of the last 90 as well as some still shots from the camera. The problem occurs at the beginning where the water backflows up the opposing line towards the other toilet. The camera entered system from A and the flush came from C. The backflow goes~3 ft (back up A) and then slowly drains down but leaves the solids behind

Thanks

 

[Jeff H Young]

the 2 inch lines entering double wye can run constantly no back up? looks l;ike a long sweep at N, Shane says the stoppage begins at D .
Shane in your pictures with the first post it looked like you took the double wye out ? and you said water goes up the other branch even with double wye removed?

 

[Reach4]

What is on the middle double-whe input at B? If a threaded cleanout, maybe you could drill a hole thru the sillplate and insert a pipe with an adapter that threads into that wye and gives an outside cleanout access. I am not sure how practical this would be.

An outside cleanout could make the lack of slope less painful.