Finding your septic tank
Please note that these are just suggestions based on experience. Every home is different, and every installer has his own ideas. In addition, these tips are based on our experience finding tanks in our working area. I cannot say what might be typical in other Provinces or States. It helps to put oneself in the shoes of the original installers. Septic tanks are often large and heavy, and require a crane truck.
This means that they are often in an area accessible to a large truck. Water flows downhill, so this rule may not apply if it is a multilevel home on a sloping lot. In this case, especially if there is plumbing on the ground floor, the tank would most likely be at the low end of the home, whether there is truck access or not.
If your home is on a street with similar homes of a similar age, the tanks might be in the same location. Try asking some neighbors.
As a rule, on a typical older home, tanks are 3 to 10 feet away from the house, in the back yard, near the main bathroom window.
Find the main bathroom window. On a two level house, they are often one above the other, and the plumbing stack will usually come out of the house outside the bathroom.
Look on the lawn for disturbed soil, dead grass, a depression or high spot in the soil, a concrete paver or other signs. Some homeowners will use a pencil, paint or felt pen to mark the location on the foundation of the house. It might pay to walk around your home and look for an arrow or measurement on the foundation wall.
Try looking in the basement for the pipe coming out of the house. It is usually 4 inch black ABS plastic or cast iron. If you see 2 inch pipes, see how they slope if possible, as they will join the big 4 inch at some point. If you see the large pipe going into the floor, you know it is coming out under the footing. These tanks are often very deep.
If there is a cleanout inside the house, the cap can be removed and a tape measure or fish tape inserted and pushed down the pipe until resistance is met. This may be the tank, or it may be a pipe elbow. Either way, it gives an idea how far from the house the tank might be.
WARNING – WARNING – WARNING! If the system is backed up and the pipe is full, you will have a flood if you remove the cleanout cap. Think very hard before taking this step!
At this point, whether you have any clues or not, you need to do some probing. The common method is a piece of rebar and a sledgehammer, but if possible, make a probe out of a piece of 1/4 or 5/16 inch steel rod and weld a T handle to it. It will be much easier to push into the ground. If you have the time, wait until rain soaks the ground, or run the lawn sprinkler to soften the soil. The wire will bend, but can be easily straightened. Start in the most probable areas and probe in a grid pattern, marking as you go so you don’t miss or redo areas. Try to determine the probable depth of the tank before starting, and be sure to probe to an adequate depth each time. Without practice, a large rock will appear to a tired discouraged prober as the lid of a septic tank. Before grabbing the shovel, mark the depth precisely on the probe and continue outward from that location. If it is the tank, you will hit concrete at the same depth in a large area. Once you are sure it is the tank, probe in four directions to find the outline of the tank. A discussion with neighbors who are familiar with their tanks will give you an indication of the probable lid location. It is easier to dig once in the probable area of the lid than to dig at random, only to find you are at the wrong end of the tank.
If the above tips do not result in success, you will need to resort to better technology. The easy way is to bring in the excavator, and start random digging. It is surprising how many people do this, only to find the tank 6 inches down, outside the bathroom window. The resulting carnage in the backyard must be seen to be fully comprehended.
We prefer more scientific methods. We use a magnetic locator to look for metal in the lawn, starting in the obvious spots. Steel in the tank lid will give a very good signal. You may be able to rent one of these from a contractor rental company.
If at this point you are having no luck, it’s time for an electronic tracer. This is a fairly specialized piece of equipment probably not available to most homeowners. We use several different types, as well as a color pipe camera with a radio transmitter built into the camera head.