How to Make a Septic Tank Drain Field

  • 4-8 hours
  • Intermediate
  • 100-500
What You'll Need
Perforated pipe
Thin gardening-type cloth
What You'll Need
Perforated pipe
Thin gardening-type cloth

If you have a septic tank on your property, you will need a septic tank drain field, also known as a leach field or leach drain to complete the system and make it functional. While all septic tank drain fields require regular inspection, you can save a lot of money by digging one yourself.

Step 1 - Choose Your Site

You will want to choose a site that is away from the house, but close to the tank. The field should be at least 10 feet away from your edible garden and any water, such as a lake, river, or well.

Step 2 - Contact the Authorities

Verify if you need a permit to build the septic tank drain field or if you need to have the site inspected prior to starting work. Digging the field is a lot of hard work, but having to remove it and start over again is even worse. Verify all of the relevant laws and regulations prior to starting this project.

Step 3 - Make Sure the Soil is Appropriate

Even if it's not required, have the soil tested in the area. If the absorption capacity is too low, you will have trouble with back-ups. It's best to find this out before you dig.

Step 4 - Start Digging

drain field

You will need to dig either four two-foot long trenches or two 50-foot trenches for a 1,000-gallon septic tank. Each trench should be three to four feet wide and equally deep.

Make your trenches so they tilt downward slightly, but no more than a 1/4-inch incline for every eight feet you have. You do not want the wastewater to pool at the bottom and rise up.

Step 5 - Place Gravel

Once the trenches are dug you will put at least 1-1 1/2 inches of gravel along the bottom of each trench. This allows for drainage under the pipe.

Step 6 - Add the Pipe

Place the pipe from the septic tank all along each trench. Use the clamps to hold the pipe in place at the septic tank drain so it does not shift and misalign.

Step 7 - Add More Gravel

Once the entire pipe is in place, fill the trench with another one to three inches of gravel and let the gravel work its way down around the pipe.

Step 8 - Add the Cloth

exposed sewer pipes

When you have laid the pipe and gravel, drape your cloth over it. The cloth can be any type that breathes. Its function is to keep dirt and sand from blocking the drainage from the gravel.

Step 9 - More Dirt

When you are done with the pipe and gravel, your next step is to fill the rest of the trench in with dirt so your field is level with the ground around it. You will need to wait two weeks for the ground to settle. When the ground settles, you will probably need to add more dirt to level your field.

Step 10 - Plantings (Optional)

There are several plants that will do well in the septic tank drainage field to keep it from looking like a complete eyesore. Keep in mind you cannot aerate or till the soil. You also cannot add more than two to three inches of top soil. The plants you can use that require very little water and have shallow root systems include Japanese surge, carpet bugle, periwinkle, Irish moss, and some strains of wildflowers.


Many health departments require a percolation test to establish suitability of drainfield soil. Depending on your area, the law may call for a licensed professional or agency to perform this test for you. Research your local rules regarding septic tank usage.

In addition to the potential legality issues, if the septic tank drain field is installed incorrectly you will have a back-up problem in the tank.

Septic Tank Drain Field FAQ

How deep should a drain field be for a septic tank?

A drain field, or leach field, is always buried in the ground but the depth varies. Drain lines should be at least six inches below the surface of the soil but may be deeper, though they don't need to be so deep they are difficult to access.

What kind of pipe do you use for a septic drain field?

Leach field pipes, which are a type of perforated PVC pipe, are used for septic drain lines. This may also be called corrugated pipe.

What slope is needed for septic pipe?

Water moves downhill, which is just a simple law of physics. You can't get water to naturally move uphill and it doesn't move at all when it's level, so you need to lay drain pipe with a slight slope to it so that the water will flow through the pipe.

Drain pipes should have a slope of one-fourth an inch for every foot. This will prevent clogs and keep everything flowing out through the pipe, which is just what you want.

What should drainage pipe be laid on?

You don't have to fill your trench with gravel before placing a drainage pipe but it is a good idea to put down landscaping fabric, which prevents weeds and plants from growing. This will help keep stuff from growing around the drain pipe.

How big should my drainage pipe be?

Drain pipe is usually four, five or six inches in residential plumbing. All of these sizes are super simple to find at home improvement stores because these are all basic sizes.