# Pitch on drains and sewer



## madmantrapper (Jun 29, 2017)

I'm not a plumber by trade, I am a cabinetmaker and home builder. I have always been taught the pitch on drains should be between an 1/8 and 1/4 inch or more then a 45 degree down slope. I was taught that anything more or less would cause the solids to be left behind. Today I was having a septic system installed on a new build the guys had the 4" line sloped about 1 1/2 inches per foot for about 40 feet. I mentioned what I thought I knew and was told that it was an OLD WIVES TALE.

What do you guys think?


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## MarkJames (Nov 25, 2012)

madmantrapper said:


> I'm not a plumber by trade, I am a cabinetmaker and home builder. I have always been taught the pitch on drains should be between an 1/8 and 1/4 inch or more then a 45 degree down slope. I was taught that anything more or less would cause the solids to be left behind. Today I was having a septic system installed on a new build the guys had the 4" line sloped about 1 1/2 inches per foot for about 40 feet. I mentioned what I thought I knew and was told that it was an OLD WIVES TALE.
> 
> What do you guys think?


I'm with you. I recall no more than 1/2" per foot.


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## Big Johnson (Jun 2, 2017)

madmantrapper said:


> I'm not a plumber by trade, I am a cabinetmaker and home builder. I have always been taught the pitch on drains should be between an 1/8 and 1/4 inch or more then a 45 degree down slope. I was taught that anything more or less would cause the solids to be left behind. Today I was having a septic system installed on a new build the guys had the 4" line sloped about 1 1/2 inches per foot for about 40 feet. I mentioned what I thought I knew and was told that it was an OLD WIVES TALE.
> 
> What do you guys think?



1/2" is most desired

Code in my area is:

1/8" -1/2" for 4" or larger
1/4"-1/2" for 3" or smaller.

That main drain should be sloped 1/2"/ft then drop on a 45 to get down to the tanks. Is it being inspected by the sanitarian?


Those tanks are either deep underground or the house is up on a hill.


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## madmantrapper (Jun 29, 2017)

Yes the inspector just looked the job over and signed off. I think I am going to call there and make an inquiry tomorrow.


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## Golden view (Feb 16, 2012)

Old wive's tale.

I've watched scopes on all kinds of slopes (2" per foot, etc). The only problem is when it goes up hill. 

Big mains have a max slope, something like 8% but that's for velocity and erosion problems. They can also have a very shallow minimum slopes, maybe 1/2" in 100 feet.


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## tjbnwi (Feb 24, 2009)

If it is the line from tank to field, there should be no solids what so ever in the line.

Pitch as long as it's downward will not matter.

Tom


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## griz (Nov 26, 2009)

one hell of a turd if your worried about blocking a 4" pipe with that fall....:whistling


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## Big Johnson (Jun 2, 2017)

tjbnwi said:


> If it is the line from tank to field, there should be no solids what so ever in the line.
> 
> Pitch as long as it's downward will not matter.
> 
> Tom


If it is it would be 2" pressurized. They won't allow 40' of gravity from tanks to drain field where I'm at.


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## Big Johnson (Jun 2, 2017)

griz said:


> one hell of a turd if your worried about blocking a 4" pipe with that fall....:whistling



Not one turd, the concern is the one turd (and wads of TP) will get left behind to catch the next turd/TP. I don't think it's all that likely under normal use but wrong is wrong. I'm sure T/TP gets hung up all the time when piping is pitched correctly as well. The next flush of #1 moves it along.


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## greg24k (May 19, 2007)

Old saying and a word of advice "Don't let the water flow faster than your crap":laughing:

That being said 1/4" minimum slope assures sufficient flow velocity to move solids. Flow of 2' per second is the minimum recommended for soil and waste lines.


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## Fouthgeneration (Jan 7, 2014)

2006 IRC"The maximum slope of a horizontal combination waster and vent pipe is 1/2" per foot.
- P3111.2.1 Slope.The horizontal combination waste and vent pipe shall have a maximum slope of 1/2 unit vertical in 12 units horizontal (4-percent slope). The minimum slope shall be in accordance with Section P3005.3."

Use 45 degree and vertical stacks instead of any slopes > 4% on waste lines.....

With a 1% slope you probably could of had a basement toilet.....?

55 inch lower height of sewer line leaving the house......


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## madmantrapper (Jun 29, 2017)

Fouthgeneration said:


> 2006 IRC"The maximum slope of a horizontal combination waster and vent pipe is 1/2" per foot.
> - P3111.2.1 Slope.The horizontal combination waste and vent pipe shall have a maximum slope of 1/2 unit vertical in 12 units horizontal (4-percent slope). The minimum slope shall be in accordance with Section P3005.3."
> 
> Use 45 degree and vertical stacks instead of any slopes > 4% on waste lines.....
> ...


Thanks I should have looked there first. County inspector said its all good.


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## Golden view (Feb 16, 2012)

Fouthgeneration said:


> 2006 IRC"The maximum slope of a horizontal combination waster and vent pipe is 1/2" per foot.
> - P3111.2.1 Slope.The horizontal combination waste and vent pipe shall have a maximum slope of 1/2 unit vertical in 12 units horizontal (4-percent slope). The minimum slope shall be in accordance with Section P3005.3."


This is the vent section of the code, this applies only to combination waste and vent.

You want P3005.3. Only specifies a minimum.


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## Seven-Delta-FortyOne (Mar 5, 2011)

Well, no, it's not an old wives tale, but, it is not critical in every situation.

First, slope is based on pipe diameter. Larger pipe generally gets a flatter slope. It's all about keeping it to 2' per second.

Second, distance matters. A 17' waste line from a lav to the building sewer, could probably be just about any slope, as long as it's downhill. Thousands of feet of city sewer line? No, it's needs to be much more accurate, or you would have very genuine problems.

I did the underground on 70-something space RV park many years back, and for the really loooong runs, some of those lines were spec'ed at 1/16" per foot. It was all 6 and 8 inch line, though.

So all of you are right. :clap: To some extent. :whistling




Delta


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## Fouthgeneration (Jan 7, 2014)

"Waste & Vent....." I still be worried a #2 flush might "sweep" the pipe , creating a vacumn pulse that would break a seal(s) on some water traps, releasing sewer gases.....

installing a vent at each end of the out of code pipe should prevent that, the bigger the better, 3" not 2".

Unvented high slope sewer pipes Might create a greater than 1 inch water column air pulse..... defeating the water traps exposed to it.


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## farmboy555 (Aug 13, 2006)

Going into the septic tank or pipe coming out? I'm a installer and from house to tank 4" pipe 1/8" -1/4" per foot drop are the requirements in my area


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## madmantrapper (Jun 29, 2017)

Man there sure are a lot of conflicting stories on this, even among the county inspectors. Talked to a few on different jobs lately and all say something different.


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## Fouthgeneration (Jan 7, 2014)

Do you under stand how the unvented run to your septic pre filter could cause air pulses that cause your home to fill with sewer gases?

low pitch larger sewer/ drain pipes normally are self vented, when sloped too much the self venting goes away when the flush pulse mass fills the pipe bottom to top.

A HIGH volume vacumn preventer could be installed at the home's exterior clean out stub to mitigate the harmful suction pulses. but why not rub the ignorant puppy's/ want to be-plumber in his mess, and have him bring your septic line to CODE so you can sell it as is? 

As a concerned citizen, you do want to stop anymore neighbors suffering the economic and health harm this ignorant plumber is creating by not following a National rational plumbing code....

A quite word with the local inspector and mention they are on the hook to for failing to properly perform their office and are liable for faulty permitted work of the past inspections of the non-complying as a person and as public office.

Sewer gases are long term TOXIC, they'll make you sick and dumber.:blink: Sewer gases are killing and making ill far more Americans then the phony Radon gas issue.


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