How to Construct a Small Septic System

Co-authored by David Balkan

Last Updated: December 7, 2024 Fact Checked

Most private septic systems are made up of two parts: the holding and digesting tanks, and the dispersal field.^{[1]
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United States Environmental Protection Agency
Independent U.S. government agency responsible for promoting safe environmental practices

Go to source} As the first holding tank fills up, the liquid waste will transfer to the second tank. Once the second tank fills with liquid, it will disperse into the soil below it. The system shown here is a small system, designed for limited use by two people with no laundry. The tank is much smaller than required by building codes, and the design is missing some important items such as internal baffles and a qualified site assessment. This system uses two 55 US gal (210 L) drums, as opposed to the 1,000–2,000 US gal (3,800–7,600 L) tanks used for a standard home septic system. The system also has a dispersal field about one third that of a large home.

Property owners planning a system similar to this one should be aware that this system would not pass inspections from any public health department in the USA and could subject the owner to a fine if the system was discovered in use.^{[2]
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Research source} On the other hand it is better to safely dispose of waste than not to. Today's water-saving toilets use less than two gallons per flush. This system will handle such a load. For people living in places without septic treatment, it could be a lifesaver.

Part 1

Part 1 of 3:

Cutting the Tanks

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Measure the outside diameter of the toilet flange you’re using. Place the hole against the edge of the drum so you can easily connect them to pipes. Use a saber saw to cut through the drums.
Push the flanges into the top of each tank so they fit flush. Screw the flanges into the tanks so they don’t move or shift after you place them.

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Place the hole about 4–5 inches (10–13 cm) down from the top of the drum and make sure it lines up with the hole on top of the tank. Cut the hole with a saber saw or a hole saw.
Find the center line running through the middle of the hole on top of the drum. Make 45-degree angles from either side of the centerline and mark it on the second drum. Use a saber or hole saw to cut through the side of the barrel and make your holes.

Part 2

Part 2 of 3:

Placing the Tanks Underground

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1
Dig a trench that’s 4 × 26 × 3 ft (1.22 × 7.92 × 0.91 m). Use either a shovel or an excavator to make a hole in the spot where you want your tank. Keep digging until the hole is 4 feet (1.2 m) wide, 26 feet (7.9 m) long, and 3 feet (0.91 m) deep.^{[3]
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- You can usually rent excavators for digging from a heavy machinery supply store. Check for equipment rentals online.
Make sure the drum is level when you set it down. Check that the top of the drum is at least 4 inches (10 cm) below the surface.
Make your hole the same diameter as the drum you’re placing in it so it has a tight fit and doesn’t move around.
Level the hole with gravel until the 90-degree bend fits from the hole in the side of the top drum to the toilet flange of the lower drum. Dry-fit the 90-degree bend between the 2 drums to see if the holes line up well. Dig the hole slightly deeper if you need to make the pipe line up better.
Cut the ABS pipe pieces, or nipples, with a hacksaw. Fit the pieces into the bend and use PVC glue to secure them in place.
Fit the end of the 2 ¹⁄₂ in (6.4 cm) nipple into the side hole on the first drum. Make sure the nipple on the other end lines up with the hole on top of the second drum.
Use PVC glue to secure the bend in place. Don’t worry about the connection to the first drum yet since you’ll connect it later.
Use your PVC glue to secure a nipple to the end of the Y-bend. Align the angled pipe on the Y-bend so it meets the incoming waste line, and glue it into the toilet flange.
Cut and glue 2 ¹⁄₂ in (6.4 cm) nipples to one end of the 45-degree bends at and insert them in the side of the lower drum. Point the ends of the 45-degree bends so they’re perpendicular to the bottom of the trench.

Part 3

Part 3 of 3:

Connecting the Drain Pipes

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It doesn’t matter what kind of stakes you use. Drive the stakes into the ground using a mallet or a hammer.
This will help make sure you create sloped drain pipes so your tanks can empty out.
Use your hammer or mallet to drive the stake down until it’s the same height as the first.
Pound the second stake down until the level is balanced. The second stake is now 1 inch (2.5 cm) lower than the first, or ¹⁄₄ inch (0.64 cm) lower per 1 foot (30 cm).
Continue adding stakes down the rest of the trench every 3 ⁷⁄₈ feet (1.2 m) from the last one so the stakes slope away from the drums.
The gravel will now slope away from the drums at ¹⁄₄ inch (0.64 cm) per 1 foot (30 cm) of horizontal distance.
Slide the ends of the drain pipes into the 45-degree bends on the lower drum. Make sure the holes in the pipes face down so liquids can soak back into the ground.
Adjust the slope by adding or removing gravel under the pipe.
Use a 2-part epoxy or silicone caulk for the best seal on your drain pipes. Try using flex pipe for this, so that if the ground shifts it will give a little.
Bury the trench to the top of the bottom drum with the remaining gravel.
This will prevent the soil from seeping into the gravel and ensure that you maintain good drainage on your tanks.
Make sure the ground is level when you finish filling in the area with your soil. Leave the top pipe from the first tank exposed so you can easily access the tanks if you need to drain them later.
Pour the water directly down the exposed pipes from the top drum. Continue filling the drum until it’s full and place a cap on top to seal it.^{[4]
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University of Missouri Extension
University of Missouri program dedicated to research-based, practical public education

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What is considered low usage?

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Low usage is under 125 gallons per day.

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What is the purpose of the 'y' elbow on the first tank? Is that left open or sealed when completed? If left open, won't it stink?

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That's your clean out, it takes a threaded cap or plug.

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How much water do you fill it with?

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The key word is "fill." Continue to place water into the drum until the level no longer increases.

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Tips

Instead of a 90° elbow, you should put two of them together, to form a U. That way the end that's in the first barrel will be pointing towards the bottom of the tank. Add a short section of straight pipe to this, extending it a few inches deeper towards the bottom. Solids either float or they sink. They don't stay around the middle. This way, the solids don't ever make it to the second tank, only the broken down liquid waste. The same should be done for each of the drainage pipes coming from the second barrel. Just to make absolutely sure that no solids make their way into the world leach field.

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The horizontal side of the "Y" connects to the waste source, and should be fitted with a connector that fits the source supply line.

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30% of the waste goes down in the ground and 70% is evaporated by sunlight. Don't compact the soil since it messes up the evaporation process.

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The advice in this section is based on the lived experiences of wikiHow readers like you. If you have a helpful tip you’d like to share on wikiHow, please submit it in the field below.

In some states and counties, it's not legal to build your own septic system. You need to hire a licensed and registered contractor who will comply with septic system codes. Consult your local laws before building your own septic tanks!
If you regularly use a septic system treatment (like RID), it will help keep the tank from needing to be pumped so often.
Try to use toilet paper as little as possible. In my home, I bag all my toilet paper except for the very dirty pieces.

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Warnings

Don't drive over the area that contains the drums.

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This is a very small capacity system. This is not designed to meet the needs of a large household.^{[5]
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United States Environmental Protection Agency
Independent U.S. government agency responsible for promoting safe environmental practices

Go to source} It is designed for a small travel trailer and two people. To maximize the life of this mini system, do not put anything in the septic system except water, human waste, and toilet paper. Otherwise, you may have to pump the upper drum once a year or so. The system shown here only needs to be pumped twice in 5 years.^{[6]
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University of Missouri Extension
University of Missouri program dedicated to research-based, practical public education

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Follow local Septic Regulations when constructing a septic system. It is illegal to install a septic system without a permit. The permit will detail the local requirements for installation of a septic system.^{[7]
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Don't place your septic system too close to trees, as tree roots will grow into your line, and cause them to clog and with time, cause harm to your system.^{[8]
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