Help with pitch of line from house to septic tank

15 years ago

Thank you all for the great advise I've picked up here as were building a new home.

We're excavating for our leach field today, which will be installed tomorrow. A backhoe operator is here to do that work and he said the pitch of the line from our house to the septic tank is too steep. That the septic tank is set 2" too low for the outlet from the house.

I know 1/4" drop per foot is ideal for that line.

And a level does show that in the last 4' of the line (which is all that's not buried at this point), drops 3" in that 4', rather than just 1".

This line from the house to the septic tank is 35'

Will this be a major problem down the road?

Thank you for any advise.

Featured Answer

bus_driver

15 years ago

The whole discussion is at the site linked below. Here is an excerpt.
"kordts
11-29-2006, 07:50 PM
"Pretty much the reason for the 1% to 2% slope is so that the water floats out the waste. If it is too steep the water can out run the waste and contribute to a clog. The big reason for a y rather than a 90 is so that you can get a snake down it easier to clean out if needed. I'm sure it is also to keep the solids flowing rather than slamming into a corner and getting stuck there. Of course, the smoother the inside of the pipe and the fewest ridges of any kind...the better and less for "stuff" to get hung on."

randyj,
that's wrong. Water doesn't outrun waste. There have been university studies on this. I have seen many long runs at steep angles, and they don't clog up. The code calls for minimum pitch, not max."

Here is a link that might be useful: Forum

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Comments (6)

bus_driver
15 years ago
"he said the pitch of the line from our house to the septic tank is too steep." Pure baloney. No code prohibits lines that are steeper than code minimum. 3/8" per foot would be better. Make the line slope equally along the entire length between the house and the tank. A 1.6 toilet will not fill a 3" or 4" line completely with a slug of water. The toilet outlet is often about 2" diameter. If the solids will continue to move along a pitch of 1/4" per foot, why would they stop moving if the pitch is greater? What force would stop them at 3/8" pitch but not at 1/4" pitch? ? Newton's First Law of Motion.
"I know 1/4" drop per foot is ideal for that line." Not ideal, but probably code minimum for your area.

Here is a link that might be useful: Newton
imthegc
15 years ago
If you get it too steep the solids will build up in the pipe. 1/4"/ft is plenty IMO
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bus_driver
15 years ago
Please show me just one authoritative source of information supporting such a claim. Why do steeper pitches promote clogging? And if the statement above is true, why do vertical pipes seldom clog. And if the above statement is true, why are the codes not addressing the "problem"? Codes typically define vertical as any angle exceeding 45 deg or more to the horizontal. Do rolling automobiles stop faster on steep downslopes? The same physics apply.
bus_driver
15 years ago
Many of the do-it-yourself plumbing books repeat this myth about steeper slopes promoting clogs. It is one of those legends that probably will never die. If it was a problem that really exists, the plumbing codes would carefully address it. To that end, look over this code (PDF) in it's entirety to see how well it does address plumbing issues. And look at 11.3 on page 147 to see how the pipe slope matter is addressed. And note the uniform slope as I suggested in my first post.

Here is a link that might be useful: Plumbing code
elbartee
Original Author
15 years ago
Thank you all for your help here.
The thought of addressing a septic tank set too low was quite daunting.

We found other work to keep the excavator busy last weekend and will get the leach field in next weekend instead.

Help with pitch of line from house to septic tank

bus_driver

Comments (6)

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imthegc

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Help with pitch of line from house to septic tank

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Comments (6)

bus_driver

imthegc

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elbarteeOriginal Author

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