You can narrow your search down by starting with four places where the septic tank is NOT located:

1. It will not be directly next to the house because the tank is required to be a minimum of 5 feet away.
2. If your drinking water is provided by a well on the property, the septic tank must be located at least 75 feet from the well. So when the well is in front or right side of your house, the septic tank and drainfield will be in the back or left side, and vice versa.
3. It will not be in an area with large trees or heavy foliage.
4. The septic tank will not be under a driveway, patio, or deck; or, at least, it is not supposed to be. It is remotely possible that a previous owner built or paved over the tank.

 With those areas eliminated, here’s some more clues to get you closer:

1. When a septic system is failing, the grass is really green and the ground is moist over the drainfield, because of the nutrients leaching into the ground that should have been contained within the tank. But even a septic system that is functioning satisfactorily will make the grass above it just a little greener. This is one way that septic tank pumpers begin their search for the tank, which will be located between the slightly healthier patch of grass and the house.
2. A septic contractor must provide a site plan/diagram to the local office of the Florida Department of Health when submitting the permit application for installing a new septic system. Other states have a similar requirement, but possibly with a different agency. It locates the septic tank and drainfield in relation to the house, with dimensions, and they keep a copy on file that you can request. Also, the previous owner may have a copy of the diagram for you. 
3. If your home is located in a low area with poor soil percolation, the large mound of soil in the yard is an above-ground drainfield, and the septic tank will be near it and towards the house.
4. A large house, especially one with a ranch-style floor plan that is long and narrow, may have two septic systems at opposite ends of the house. You may need to be looking for two tanks.

    If you are pretty sure where the tank is located, you can probe the ground in that area with a metal rod to find it. If there is any underground electrical cables in the area, make sure there is a non-conductive handle on the rod. The top of the tank is usually 2 to 4 feet down. After you get the first positive hit, you can use the probe to determine the location of the edges and shape of the tank.

    When none of the above clues work and a diagram is not available, it’s necessary to locate the main outflow pipe below ground with your metal rod and follow it to the tank. Sometimes this takes a while. The main drain pipe will start at the outside wall of a bathroom or kitchen, and the most likely location will be where a wall between an adjoining kitchen and bathroom meets the outside wall of the home. If the pipe comes out of the wall above ground, start following it there, but a cleanout in the ground near the house (like in the photo below) is another way to locate the pipe underground. Some homeowners mark the location of the tank lid with a bird bath or other yard ornament to make it easier to find it next time.

    Then there’s the easy way: call a septic contractor, order a pump-out, and let them find it for you. A pump-out every five years is recommended and, if you are about to buy the home and within the inspection period, you can request a septic system inspection report for not much more than the pump-out.

    Also, see our blog posts How often should I pump out the septic tank? and How much does a septic tank system inspection cost in Florida? and Do I have to get a larger septic tank when I build a home addition? 

• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 

  To learn more about septic tank systems, see these other blog posts:

• What are the building code requirements for gray water reuse in Florida?

• What can I add to my septic tank to help it work better? 

• Why do septic tank contractors want you to get rid of your kitchen disposal?

• How can I tell if a house is connected to a septic tank system or sewer?

• Does a septic tank have to be re-certified if a house has been vacant for a while? 

• What is a grinder pump? 

• Should I call a plumber or septic tank contractor when my septic tank backs up into the house?  

• Where is the septic tank? Are you going to inspect it? 

• Can a house have more than one septic tank? 

• What is the difference between gray water and black water in the plumbing code? 

• Is it alright to disconnect the washing machine drain from the septic tank and divert it to the ground in the yard?

    Visit our PLUMBING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.