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Septic Tank Elevation

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• #278548
MasterPlumbers
Keymaster

What is the minimum height difference between the top of a septic tank or its inlet pipe and a basement floor? The tank is presently 221/2 feet from the house outside wall and the existing basement floor is nominaly two inches above the top of the septic tank.

• #298736
TheLocalPlumber
Participant

How do you know, did you shoot a level the 22 and 1/2 feet to determine the 2″ diff?
The basement floor is not your measurement, it should be lower than that if the pipe is in the ground. Which means that there is almost no, or no pitch to the top of the tank.
Now I am guessing that the inlet is lower than the top of the tank, how much lower?
A 4″ sewer line should have a slope of at least 1/8″ to the foot, which means that 22-1/2′ should have a total pitch of 2.8″ minimum. And 5.6″ maximum.
So measure the depth of the inlet to the tank, from the top of the tank. And then, if you really want to get exact, dig a hole outside the house to locate the depth of the sewer as it leaves the house. Subtract depth of the sewer pipe when exiting the house from the depth of the inlet pipe to the tank. This will give you the slope of your sewer pipe to the tank.
Does it fit into the above parameters? 2.8″ min.-5.6″ max.
Good Luck.
Bill
The Local Plumber
Tustin, California
http://www.TheLocalPlumber.com

• #298737
Guest
Participant

Yes I shot the levels with a transit. The 4″ sewer line currently exits through the basement wall 26″ above the concrete floornd the center of the inlet pie to the top of the tank is 10″. This gives me a fall of 38″in 22′-6″(over 1 5/8″ per foot). I intend extending the house out on the side where the septic tank is. This is what promted the question of the septic tank to basement floor question.

• #298738
TheLocalPlumber
Participant

Plenty of pitch. In fact too much pitch can be just as bad as not enough.
It sounds as if you have plenty of room for your plans. May I suggest that you pay a Plumbing Consultant to look at the plan and advise you on proper installation.
Bill
The Local Plumber
Tustin, California
http://www.TheLocalPlumber.com

• #298739
John Aldrich1
Participant

PMorgan, and Bill, The Local Plumber, I would like to discuss the issue of “too much slope” in a sewer line between the house and the septic tank. I have heard the warning since I first entered the septic system business 26 years ago. It has been said that the water will “out run” the solids if the slope of the sewer pipe is too great. I have never experienced this phenomenon in any of the systems that I have installed, but if it ever does occur, the several cleanouts installed in the pipeline can be accessed to either “jet out” or “snake out” the obstruction.

I have designed, and installed hundreds of septic systems in the rugged mountains of Colorado where there was no choice but to have a very steep slope in the sewer line between the home (usually sited on top of a solid rock outcrop to obtain the very best view) and the septic tank, or sealed vault. On a few of these installations, portions of the sewer lines were vertical out of necessity. On some installations the sewer lines were extended 400 or 500 feet in length with as much as 150 feet in elevation differential.

Bill, have you ever personnally seen a clogged sewer pipeline because it was installed at too steep of a grade?

In my view, and in the view of the onsite system regulations in Colorado, there is no maximum slope to exceed in the installation of a sewer line. The minimum slope however is 1/8 inch per foot (1/4 inch per foot is preferred). JWA