I am looking to connect my shop bathroom to the septic system of my house. When I poured the slab years ago, I put in 4" plumbing for a toilet and sink. I did some measuring and its 169 feet connection point to connection point with a total drop of 53". I think the pitch is ok at 5/16" per foot. I wonder if there is any difference in using 3" or 4" drain pipe over that difference? I usually lean to the side that bigger is better but not sure if it affects how it works over a long distance.
sewer line pitch and size
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ODIS
Well-known member
Would keep the 4" line all the way to your tanks with appropriate clean outs. A plumber once told me that he has never had a call back due to "too much pitch."
Ody.
Ody.
Falcon67
Well-known member
1/4" is what is considered normal. Too much slope will have an effect as the liquids will run off too fast and leave the sold waste behind. I know a plumber and he HAS had calls that were from too much slope.
mrobins297aaa
Well-known member
1/8" per foot
aka Larry
Well-known member
I'm in the sewer (design) business and that is not true. Too much slope will let the liquid 'out run' the solid and that's not a good thing. For a sevice line (4") I'd use 1/4"/ft if you have the depth. 1/8"/ft is the minimum.
mrobins297aaa
Well-known member
I've heard that also
ctb
Well-known member
I put in a couple of my own sewer lines for a couple trailers that I set up and the code said 1 in 4 (Canada). Never had a problem with them.
1jjpop
Well-known member
Put in sewer line from my house to sewer hook up in street . Used 6 '' pipe never had any trouble ,6 '' don't cost much more then 4'' pipe .Went near trees & got sack crete & put around joints. Been 18 years since I did work , no problems..........
As it is now if I ran a straight line between the 2 it would be about 5/16" per foot. A 1/4" per foot would be a drop of 42.25, and I have 53". Would it be better to run it at a 1/4" per foot and make up the difference in the last 10 or 20 feet?
csp
Well-known member
That extra 1/16" per foot isn't going to make a difference. You want 2% grade and that puts you at 2.6%.
plain2car
Well-known member
1/4" per foot is my experience as well
larry4406
Well-known member
Plumbers here in northern VA use 1/4 inch per foot slope with sewer laterals run as shallow as 1/8 inch per foot. My garage sewer lateral is run to my house at 1/4 inch per foot, comes thru the house basement foundation wall, and then ties in to a 4" stack in the house, flows throw the house ground works under the slab, and then to the septic tank.
In my case, much shorter distance to the house vs to the septic tank.
In my case, much shorter distance to the house vs to the septic tank.
Kevin54
MEMBER EMERITUS
When I helped my FIL, everything was ran at 1/4" per ft.
bigdav160
Well-known member
I read on the interweb, so you know it's true, that there is a minimum slope but no maximum.
There was a long thread on it in a plumbing forum.
Perhaps the code nazis could confirm or deny.
There was a long thread on it in a plumbing forum.
Perhaps the code nazis could confirm or deny.
csp
Well-known member
Regardless of code, it's been proven that water will outrun the turds if the slope is too steep (as already stated in this thread). One of my good friends owns a septic business and has run into this several times.
Tim Kennedy
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Worked a lot of jobs replacing sewer lines when I was younger & heard the same story about too much pitch being bad -- but with todays plastic pipes being so slick on the inside it really isn't a problem. Looks like a 1/4" per foot is the norm but remember -- water will flow in a level pipe & 1/8% slope [1/8" drop in 100 feet] is all that is needed. My home system was put in with mininum slope until it connects to the main & then it drops10 vertical feet in a span of 3 horizontal feet & have never had a problem in 23+ years.
Matthew C Smith
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So what would you recommend as a maximum? Just trying to put some numbers in my head....
AndyA
Well-known member
The International Plumbing Code says:
1/4" per foot for pipes 2-1/2" and smaller
1/8" per foot for pipes 3" to 6"
1/16" per foot for pipes 8" and larger.
Guess you're screwed if you happen to have 7" pipe
If you're worried about too much slope, how about putting in a small vertical offset?
1/4" per foot for pipes 2-1/2" and smaller
1/8" per foot for pipes 3" to 6"
1/16" per foot for pipes 8" and larger.
Guess you're screwed if you happen to have 7" pipe
If you're worried about too much slope, how about putting in a small vertical offset?
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This is true, but what is also true is that today's "water efficient" toilets don't put a whole lot down the drain. If 4 liters (or whatever) is all you get, you better make sure your drain is set up to make the most of it. Either that, or make sure you use several gallons of water washing your hands when you take a dump in the shop.
Better yet, drink a lot of beer, and piss a lot
AndyA
Well-known member
I've laid many a "double flusher" 
1/8'' and 3'' pipe.. Todays low flow toilets dont give enough wash water like the old ones did so by using the 3'' pipe you will effectively 'deepen' the liquid that the turds are floating in.... For an example look at a cross section of 3'' pipe against a 4'' pipe. See how much wider the 4'' is? your liquids spread across the pipe instead of staying deeper and floating the turds out... Keep your lateral line at the 1/8'' per foot level the drop a little quicker towards the end of the run to tie into your other line.... Hope this helps. If you have any more questions you can message me. FWIW, I make a damn good living installing private and municipal sewer/septic systems.