PVC sewer lines - where does the slope come from?

[Stephen Tashiro]

The recommended slope for the horizontal run of sewer line is a miniumum of 1/4 inch per foot. When you look at diagrams of plumbing, you see vertical pipes meeting horizontal pipes with fittings that make a 90 degree turn. If things were set with geometric perfection, there couldn't be any slope on the horizontal pipes. So how is the slope implemented in practice?

Do people install pipes in the fittings slightly askew so the horizontal pipes can slope?

Or are the vertical pipes not set perfectly vertical?

Or are there nominal 90 degree fittings that actually make more than a 90 degree angle?

[Paul F Franklin]

Waste fittings have a 2% slope build into the fitting.

[Bill Jobe]

Waste fittings have a 2% slope build into the fitting.

I did not know that.
I do know that you don't want a drain pipe inside to drain completely dry or solids will dry out and a clog will eventually develop. Nor do you want a low spot where water can stand, causing the drain not to flow.

What I don't get is how a guy who taught me how to improve on my gluing technic manages to hold pvc being glue just 5 seconds or so without any pushout
I get pushout after 20-30 seconds. I always prime and add glue to both pieces. Twist the 2 parts about 45°.
I just don't get it.

[Ole Anderson]

If you slope all of your pipes properly, they will have no choice but to be dry when water is not running.

[Bill Jobe]

If you slope all of your pipes properly, they will have no choice but to be dry when water is not running.

I disagree. Small areas of solids will retain enough moisture that running water will wash it away. Too much slope and more water is released, causing a dry clump that restricts flow. With time you have a clogged drain.
I think the pipe should remain slightly wet.

[Dan Friedrichs]

I did not know that.
I do know that you don't want a drain pipe inside to drain completely dry or solids will dry out and a clog will eventually develop. Nor do you want a low spot where water can stand, causing the drain not to flow.

What I don't get is how a guy who taught me how to improve on my gluing technic manages to hold pvc being glue just 5 seconds or so without any pushout
I get pushout after 20-30 seconds. I always prime and add glue to both pieces. Twist the 2 parts about 45°.
I just don't get it.

There are glues that set up at different speeds.

[Ole Anderson]

Small areas of solids will retain enough moisture that running water will wash it away.
That statement is contradictory. Are speaking from experience? I have designed miles of sanitary sewers and seen a lot of pipeline videos (retired PE). As long as the slope is adequate to maintain a velocity of 2 feet per second, the pipe will self cleanse. Pipe laid too flat or with a belly will tend to have a sediment buildup in the invert. Unless you get a grease clog (a big one has been called a fatberg by the press!) or a physical impediment such as a broken pipe or roots, the pipe will self cleanse. "Running water will wash it away". https://www.theepochtimes.com/19-ton-100-foot-long-fatberg-clogs-michigan-sewer_2661577.html

[Mel Fulks]

Baltimore . Fatburg. Sounds like a story only John Waters can tell !

[Bill Jobe]

Sorry. I somehow was thinking the subject was about indoor home plumbing.

[Bill Jobe]

Baltimore . Fatburg. Sounds like a story only John Waters can tell !

Mr. Fulks fills my mouth with laughter.

[Ole Anderson]

Sorry. I somehow was thinking the subject was about indoor home plumbing. Same rules apply, just the scale is different.

[Tim Bueler]

Sounds like there's a little over thinking going on.:confused: Plastic pipe bends easily. If you have your pipe supports set up so you can anchor the pipe once glued, but not set, it will easily conform to that gentle of a slope. Even though the socket on a modern pipe fitting is tapered there is still plenty of slop, especially when solvent cement is applied, to adjust. Even in the days of cast iron hubs with oakum and lead seals (lead pipe cinch) there was enough play in the fittings to make slopes work.

I haven't looked at a code book in a long time but best I recall, for residential applications, is waste lines <3" diameter are sloped at 1/4" per foot. Waste lines 3" and larger are sloped at 1/8" per foot. I may not be remembering correctly, or the code may have changed, or it may be different by jurisdiction, or now maybe I am overthinking ;). The easiest way to know beyond a doubt is to call the local plumbing inspector. He/she will tell you exactly what they expect to see.

[Rich Engelhardt]

PVC sewer lines - where does the slope come from?
Eric - it comes from his hands -Eric of J&K Plumbing.....I tell him what I want, he gives me and estimate & I tell him to make it happen...he does & I pay him.
I have no desire to know how he works his magic, nor do I want to know.
:D :D :D

[Jim Koepke]

As long as the slope is adequate to maintain a velocity of 2 feet per second, the pipe will self cleanse.

Isn't clearing the pipe part of the reason people are supposed to wash their hands after using the toilet?

jtk

[Bill Jobe]

Isn't clearing the pipe part of the reason people are supposed to wash their hands after using the toilet?

jtk

What opportunities are mine as I struggle with great difficulty to understand the meaning of your post?

[Jim Koepke]

What opportunities are mine as I struggle with great difficulty to understand the meaning of your post?

Especially with today's toilets using a lower volume of water, running the tap while washing one's hands adds a bit more water to help in moving the solid waste along its way.

jtk

[Tom Stenzel]

...As long as the slope is adequate to maintain a velocity of 2 feet per second, the pipe will self cleanse. Pipe laid too flat or with a belly will tend to have a sediment buildup in the invert. Unless you get a grease clog (a big one has been called a fatberg by the press!) or a physical impediment such as a broken pipe or roots, the pipe will self cleanse. "Running water will wash it away". https://www.theepochtimes.com/19-ton-100-foot-long-fatberg-clogs-michigan-sewer_2661577.html
Ole has right.

I noticed that the report about the "fatburg" had the line, "From there the waste is supposed to go to a processing plant in Detroit."

Hey wait- that processing plant is where I worked. For 31 years 8 months not that I was counting.

I remember reading a reprint of an article in a wastewater treatment periodical by a Detroit engineer that described large clumps of grease that would come into the plant during rain events and damage the screening equipment. Plus the grit channels would get buried. This led him to develop an interceptor constant velocity strategy that would prevent the buildup of geases and grit in the system.

The engineer was Clyde L. Palmer. The article was published in 1940. I'm sure Mr. Palmer rubbed a digit or two off his slide rule coming up with those graphs. When I wandered into the plant a few decades later that strategy was still in place. Plus weekly pumpdowns where the water level was taken down almost to the point of pump cavitation to scour out the system. Allowing standing water to remain in the collection system to save pumping costs always came to a bad end.

We were expected to deal with whatever grease and trash arrived.

-Tom

[lowell holmes]

See this link

http://www.balkanplumbing.com/pitch-slope-sewer-line-house-drain-pipe/

[Ron Citerone]

Interesting thread. The more I learn about any profession, the more I understand how much I don't know...........................and how people who often accuse others of "overthinking" things don't know. If that makes sense.

[Jim Koepke]

Interesting thread. The more I learn about any profession, the more I understand how much I don't know...........................and how people who often accuse others of "overthinking" things don't know. If that makes sense.

A great observation Ron.

It is always the know nothings that seem to insist they know it all.

jtk

[Dylan Wyatt]

We just went through this derivation at work last week in an effort to prove we could lay a pipe flatter that minimum grade. The minimum slope of gravity sewer pipe is the minimum slope for solids to stay suspended in the liquid in a gravity sewer pipe, 2 feet/sec. This is based on the pipe flowing full and with a roughness coefficient for concrete (or clay, I can't remember for sure). In our case it is regulated by the EPA. The jury is still out on if they will approve the plans, but with simple calculations we proved that we could lay a PVC Sewer line almost 0.10% flatter than the EPA Book called for, which was critical in our circumstances.

[Bill Jobe]

A great observation Ron.

It is always the know nothings that seem to insist they know it all.

jtk

I thought I was right.
I opoligize.