Minimum Slope for 3" Waste Line

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brian sturgeon

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I just had a pole barn built. We are putting a bathroom in it but unfortunately the builder did not pay attention to the elevation of the septic tank inlet pipe when setting the grade board. The grade board which determines our finished floor height was set about 3-6" lower than it really should have been. This means that we don't have the ability to use 1/4" slope per ft and still stay low enough to pour our slab on top. The main line is basically an L. From where it enters the barn as a 3" line it runs 22' towards back of barn and then 90's and runs for another 17'. We will have a bathroom located near the end of the 17' section. We can do an 1/8 slope on this line and still be okay with having enough room to pour our pad but I wanted to make sure that 1/8 would be enough. I read some things that say it is fine and other things say it is not. I am located in IN and the county this barn is in does not really care too much with how things are done in barns like this. Please help and tell me that 1/8 would be fine. :)
 

Reach4

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It looks like it would work in Virginia:
See page 7-9 in http://www2.iccsafe.org/states/virginia/Plumbing/PDFs/Chapter 7_Sanitary Drainage.pdf

You might want to be more careful of eliminating sags than you would with 1/4 per foot. Got a bright green laser to skim across the top of the pipe to check straightness? Maybe you could have view of the inside of the pipe for sighting. I don't know how to maintain a slope during a concrete pour. Maybe use rocks or bent rebar under the pipe at sagging spots as supports?

Just thinking. I am not a plumber.
 

Terry

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1/8 is pretty sketchy.
My inspectors want 1/4"
I would consider running at a 45 instead of at a 90 to reduce the distance. It would also be one less change of direction to slow things down.
 
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