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Septic Tank design and engineering

Ef Loovium
User ID: 82468449
United States
03/15/2022 01:52 AM
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Septic Tank design and engineering
The area I reside in has low soil percolation.

Here is what works, what doesn't, and what you can do.

First, some history.

There are two types of septic tank systems historically in use in my area before standard septic tanks were in use.

First was a perforated 55 gallon drum with rocks in it.
The perforations were either from an axe or a pick, and the drum set in the ground and covered with a piece of roll roofing or shingles and loose dirt.
That's right, the paper was put in a garbage pail in the bathroom.

The second type had a typical tank, but the drain field was an area of fist sized rocks, arranged so the effluvium could evaporate. Actually, the 55 gallon drum worked better.

******* WHAT WORKS *******

A septic tank should have the exit drain lower than the input side. They are often both on the same level, but if the exit drain is lower, the tank will hold some of the fluid and give it time to drain and percolate through the leach field. Even a few inches difference helps a lot.
If the drain is on level with the inlet, the liquid can seep up out of the tank, if it doesn't drain away fast enough.

At this point you want to keep the paper and solids in the tank rather than allow them to flow out and clog up the pipes, gravel and soil that comprises your drain field.
It is MUCH easier to pump out the tank than to dig up the field.

You want a way to strain that stuff and the way to do that is with 4 inch PVC that has slots. (like with a circular saw) Slot it longways so it isn't weakened too much. You can cap it at the bottom and slot the cap or use a store bought shower strainer. Don't forget to slot or drill at the top, so it doesn't air lock like an upside down jar.

So, leaving the septic tank, you should have 4 inch PVC dropping at about one inch per 4 feet.

This isn't always easy. You can fudge the drop rate a bit if needed. But not a lot.

So you have one pipe coming out of the tank and now it needs some place to go.
The best way, I think, is to have un perforated pipe that goes out where you want it to drain. For me, it was about 60 or 70 feet.The last 10 or 20 feet should be perforated,covered in gravel and hopefully have a clean out at the end.

20 feet of perforated pipe? That's not enough right?
That last 20 feet of perforated pipe lays OVER other perforated pipes in graveled ditches. With clean outs at the far end.
So each run can be cleaned. Each one can be located by putting a wire in it.
Runs can be added without having to splice into a manifold.

Basically, the tank drains through gravel over pipes laying in gravel. Each pipe has a clean out and can be located.
Adding pipes is relatively easy.

Put some weed cloth over junction area.