How to Find a Septic Tank

Proper septic system maintenance requires knowledge of the location of the tank, which must be inspected and pumped periodically. If you aren't the original owner of your house, and you don't know where the tank is, you can probably find someone who does.

Old septic tanks can be very close to the house.

Failing that, the search for the tank is a bit like a hunt for buried treasure. Like any good hunt, this one has clues, and you reach the goal quickly if you follow them. Once you've found the tank, you need a probe and shovel to find the most important part -- the lid.

Ask Someone

  1. Consult any of the previous owners of the house with whom you're still in contact. A former long-term tenant may also know where the tank is.

  2. Look for the records of the septic system installation, which will pinpoint the location of the tank. If you don't have these around the house, call the building department of the county in which you live. Most building authorities keep these records on file.

  3. Call local septic service pros and ask them if they have ever serviced the tank at your address. This option is a long shot, but it's possible the previous owner had the tank pumped just before you bought the house; the service technician who did the job may remember where the tank is.

The Treasure Hunt

  1. Locate the main sewer outlet exiting your house and note the direction it takes. You may be able to see the pipe from outside the house, but in most cases, you'll have to find it in the basement or crawl space.

  2. Follow the waste pipe by probing at 6-inch intervals with a soil probe tool. This technique allows you to detect when and if the pipe changes direction. In many cases, the pipe goes straight from the house to the tank, and if you know the pipe direction, you can easily find the tank. On sloped properties, though, the pipe may bend, and the tank may be around a corner of the house. Always probe carefully to prevent damage to the pipe or septic tank.

  3. Determine the distance of the tank from the house with a sewer auger, if you can't follow the sewer line. Insert the auger through a cleanout in the pipe and push until it won't go any farther, which means it has contacted the tank inlet. Mark that place on the cable with masking tape, retract the auger and measure the length of the cable with a tape measure. Subtract the distance between the cleanout and the house's foundation; the result gives you the approximate distance between the foundation and the inlet of the septic tank. Wear thick rubber gloves during this operation, and sterilize the auger with bleach when you're done.

  4. Probe the ground at the approximate distance indicated by the auger, using a soil probe. You can also rent a metal detector to locate the metal parts of the tank.

Locating the Lid

  1. Probe around the tank to locate its sides and ends. Most tanks are rectangular, so once you know where the sides and ends are, you have a pretty good idea where the center is.

  2. Dig down to the center of the tank with a shovel. If you hit metal, you've found the lid; but if you hit concrete or plastic, the tank probably has two lids -- one for each of its two sections.

  3. Dig midway between the center of the tank and one of its ends to find one lid. The other lid is located the same distance toward the other end.

  4. Tip

    If you can't find a cleanout on the sewer pipe you can run an auger into the drain below the lowest toilet in the house. This requires temporarily removing the toilet. One of the advantages of using a metal detector to locate the tank is that it will find metal lids so you don't have to probe for them. Not all septic tank lids are metal; heavy-duty lids on tanks that must withstand vehicular traffic can be concrete. You can always identify a lid, however, by the fact that it has a handle.


    If the tank is old, exercise caution when working around it, especially when uncovering the lid. If the lid is old and corroded, you could fall in the tank, and that is usually fatal.

    Never open or inspect a septic tank yourself. All maintenance to the tank itself should be done by a qualified professional.