I’m adding an ADU in California. Can I connect my sewage from the ADU 18 feet away to the existing line?
DFU calculation
current sewage from kitchen and bathroom
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isherwood
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Benjamin Williams
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with the correct ADU slope you can – Ruskes Mar 06 '23 at 05:11
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Could you expand on what a "correct ADU slope" is? Not everyone knows as much as you do, @Ruskes. – FreeMan Mar 06 '23 at 19:00
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@FreeMan my answers are for the OP, post a question if you want to know – Ruskes Mar 06 '23 at 21:46
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My point is that your "answer" is so cryptic that even the OP may not have a clue what you're talking about. But, that's nothing new... – FreeMan Mar 07 '23 at 12:17
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ADU = Auxiliary (or additional) Dwelling Unit. It’s basically an addition to my house that will occupy the empty lot adjacent to the existing house structure. – Benjamin Williams Mar 07 '23 at 14:14
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I'm not a plumber but my understanding is you need the sum of all DFUs (main+ADU), plus need to know the diameter of the soil pipe (looks like 3"), then you can look up the minimum slope you'd need. e.g. For <= 36 DFUs and 3" soil pipe, the MINIMUM slope is 1/8" per foot but 1/4" per foot is preferred. It looks like you have plenty of vertical room.
More importantly, you want to minimize bends. So you probably don't want to go 18' horizontally because that would be perpendicular to the main run and require a 90-degree connection (assuming it goes out past the porch to the street on that side of the house). Instead do a longer run under bedroom-2 at 45-degrees. Don't forget to include a clean-out at the ADU, preferably outside so you can get a snake in it without entering the crawlspace.
Longer runs in plastic will require an expansion joint and make a popping sound with temperature changes due to expansion, so I would run cast iron beneath the bedroom, then you can connect to ABS with a Fernco coupling at the ADU, similar to what you have shown in your photo. For couplings that are above ground, use the steel jacketed versions, not the flexible PVC kind you have in the photo. Use two hangers per pipe (i.e. between couplings).
The ADU will require proper venting too, of course (e.g. 3" stack).
Edward Kirton
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