How to find your septic tank and drainfield

You can't maintain what you can't find. A surprising number of homeowners on septic don't know where their tank is, and they find out the expensive way: a pumper billing extra time to locate and dig, a new patio poured over the lid, or a drainfield crushed by a delivery truck. Finding your system takes an afternoon, usually costs nothing, and pays off for as long as you own the house.

Start with the paperwork

The fastest route is a drawing someone already made.

• Your local health department. In most of the country, a county or local health department permits and inspects septic systems when they're installed. University of Georgia Extension notes the health department may have a record or map of the system and will provide it on request. These records often show the tank's location, the system type, and the drainfield's length and depth. Ask for the "as-built" drawing, permit, or final inspection report for your address. Some counties have them online.
• Your closing documents. A home inspection or septic inspection done when you bought the house may include a sketch or measurements.
• Previous pumping receipts. Pumping companies often note the tank's location and depth, and some keep records by address. If you know who pumped the tank before, call them.
• The installer, if the system is recent and you know who built it.

Older systems may have no record at all. Harrison County, Indiana's health department, for example, says its septic permits go back only to 1975. UGA Extension warns that records for old houses may be incomplete or drawn on something other than graph paper. If that's your situation, the clues below will get you there.

Clues around the house and yard

• Follow the sewer pipe. Find where the main sewer line leaves the house, usually in the basement or crawlspace, on the wall facing the tank. A two-way cleanout outside the foundation points the same way. The tank sits on that line, between the house and the drainfield.
• Distance from the house. Oklahoma State University Extension says most septic tanks are about 10 to 25 feet from the house and can't be closer than 5 feet. Porter County, Indiana, says tanks there are normally about 10 feet from the house.
• Depth. UGA Extension says the top of a tank is usually 1 to 4 feet below the surface. Harrison County says 1 to 2 feet is typical but notes that some older tanks were buried as deep as 4 feet or more.
• Look at the lawn. OSU Extension notes the grass over a tank may look brown compared with the rest of the yard, because there's little soil over the concrete. A slight rectangular depression or mound can be another hint.
• Lids and risers. Newer systems often have green or black plastic lids at or above grade. Oklahoma now requires new tank lids to be installed 2 inches above ground level, and aerobic treatment units there have lids that stick up 2 inches.

Probing for the tank

If the clues get you close, a probe finds the lid. UGA Extension's method:

1. Call 811 first. Before you push anything into the ground, contact 811 so utility lines are marked. It's free, and in most states it's required before digging.
2. Start about 6 feet out from the house, directly in line with the sewer pipe. Push a thin metal rod (a soil probe from the hardware store, or a long solid rod) gently into the ground.
3. Probe every foot or two along the line. OSU Extension suggests every two feet.
4. Feel for a flat, hard surface at a consistent depth. That's likely concrete, fiberglass or plastic: the tank top.
5. Map the tank. Probe in a grid to find all four edges. UGA Extension says a typical tank is about 5 by 8 feet, though sizes vary. Mark the corners with flags.
6. Find the lids. Most tanks have an access lid over the inlet end and one over the outlet end, or one in the center. Harrison County says the lids are usually about 18 inches across.

Probe gently. UGA Extension warns not to puncture the building sewer, and to keep in mind that rocks, pipes and debris can feel like the tank.

If probing doesn't work, a septic company can run a camera with a transmitter down the sewer line from a cleanout and locate the tank from above. OSU Extension lists this as the fallback. It costs money, but far less than digging blind.

Finding the drainfield

The drainfield (also called a leach field or absorption field) is usually downslope from the tank and starts a few feet past the outlet end.

• The distribution box. In many systems, a small concrete box splits effluent into the drainfield lines. Harrison County says it's usually about 5 to 10 feet beyond the far end of the tank, about 2 feet by 1 foot, and 1 to 2 feet deep.
• Trench lines. Porter County describes typical lateral trenches as about 3 feet wide, 4 to 5 feet apart edge to edge. You may see faint stripes in the lawn, greener lines in dry weather or slight depressions. UGA Extension mentions shallow depressions in straight lines as one sign.
• Probing. Porter County notes you'll know you've found a lateral line when the probe hits the gravel that covers the pipe.

Some systems pump effluent uphill to a drainfield or mound, so it won't always be downslope. Your permit drawing settles it.

Once you find it: mark it and add risers

• Draw a map. Measure from two fixed points, such as house corners, to each lid and to the distribution box. Keep it with your house records and give a copy to future buyers.
• Install risers. Penn State Extension recommends risers, which bring the access lids up to the surface so the tank can be opened without digging. Porter County recommends them too. Every future pumping and inspection gets faster and cheaper. Make sure lids are secured so children and pets can't open them.
• Mark the drainfield. Even a few landscape stones at the corners help keep vehicles and construction off it.

Protect what you found

EPA's SepticSmart guidance says to protect your drainfield:

• never park or drive on the drainfield;
• plant only grass over and near it, and keep trees far enough away that roots won't get into the system;
• keep roof drains, sump pumps and other drainage away from it.

Don't build over the tank or drainfield either. Porter County requires septic systems to be at least 10 feet from structures, including pools, patios and fences, and doesn't allow decks over a septic tank. Local setback rules vary, so check with your health department before building anything nearby.

Our guide to caring for your drainfield covers the rest.

What not to do

• Don't open or enter the tank yourself. Septic gases can be deadly, and a person can fall in. Penn State and EPA both warn against it. Leave inspection and pumping to professionals.
• Don't dig without 811. Gas, electric and water lines often run near septic systems.
• Don't use a powered auger or stake driver to probe. You can crack a tank lid or pierce a pipe.

Next steps

Once you know where everything is, schedule an inspection if you don't have a recent one. EPA says household systems should be inspected at least every three years. Our guide to septic inspections explains what the inspector should do, and the septic pumping calculator estimates how often your tank needs pumping.