7 Signs Your Septic Tank Is Full (or Failing)

The most common signs of a full or failing septic system are slow drains, gurgling pipes, sewage odors, wet or spongy ground over the tank or drain field, unusually green grass there, sewage backing up into the house, and an alarm on a pump tank or aerobic unit. These come from the U.S. EPA's list of septic warning signs, plus the alarm that systems with a pump have. A tank that is simply overdue for pumping can cause some of them. Others point to a drain field that is no longer working, which pumping alone may not fix.

Below is each sign, what it may mean and what to do. If sewage is backing up into your home right now, start with our guide to sewage backing up into the house.

Full tank or failing system: what is the difference?

A septic tank fills slowly with sludge and scum. The EPA says household tanks are typically pumped every 3 to 5 years, and that a tank is due when sludge and scum take up more than 25% of the liquid depth or come close to the outlet. When a tank goes too long without pumping, solids can flow out toward the drain field.

A failing system often means the drain field can no longer take the water. The EPA notes that after 25 to 30 years a drain field may not work as well, and that a drain field that gets more liquid than it can take can flood, sending sewage to the ground surface or backing it up into the house. Pumping removes solids from the tank, but it may not by itself fix a drain field that is no longer working. Only a septic professional can tell which problem you have, so treat the signs below as reasons to call, not as a diagnosis.

1. Sewage backing up into the house

The EPA lists water and sewage from toilets, drains and sinks backing up into the home's plumbing as a sign of septic failure.

What to do: This is the most urgent sign. Cut water use, and avoid touching the sewage: the EPA warns it may contain harmful germs. The CDC advises keeping children and pets away from the affected area until cleanup is done. Call a septic company. For a backup into the home, the EPA also suggests contacting your local health department for guidance. In Florida, that is the county health department, or Florida DEP in Marion County. Our guide to sewage backing up into the house lists cleanup and safety steps from the EPA, CDC and Florida DOH.

2. Slow drains in tubs, showers and sinks

Bathtubs, showers and sinks draining very slowly is the next sign on the EPA's list. When you call, mention which drains are slow.

What to do: If it has been more than 3 to 5 years since the last pump-out, or you do not know, book one and ask the crew to note the sludge and scum levels. If the drains are still slow after pumping, ask about the drain field.

3. Gurgling in the plumbing

The EPA lists gurgling sounds in the plumbing system as a warning sign.

What to do: Treat it like slow drains. Spread laundry out over the week to avoid sending a lot of water at once, as the EPA suggests, and book an inspection or pump-out if the tank is due.

4. Sewage odors

The EPA lists sewage odors around the septic tank or drain field as a sign of failure. Not every odor means trouble, though. The EPA notes that a smell may come from a roof vent that lets the system's pressure equalize, which is normal, and that vents can become clogged with leaves or debris. Odors around the tank or drain field, or inside the house, deserve a closer look.

What to do: The EPA says the cause of an odor cannot be diagnosed remotely and recommends calling a septic service provider or plumber. Do not open the tank yourself. The EPA says only trained specialists should clean or repair septic tanks, because they may contain dangerous gases.

5. Standing water, wet spots or spongy soil

The EPA lists standing water or damp spots near or over the septic tank or drain field, and says soft, wet or spongy soil around the drain field, especially when there has been no significant rain, is a good indication of failure. It means effluent is coming up instead of soaking down. If the drain field gets more liquid than it can take, the EPA says it can flood and send sewage to the ground surface.

In Florida, heavy rain can make this harder to read. The rule for siting drain fields is based on the water table at the wettest time of year, and the EPA's test above is wet ground when there has been no significant rain. Tell the septic company about recent rain when you call.

What to do: Keep people and pets off the wet area and cut water use. Call a septic company and ask them to check the drain field, not just pump the tank. Do not have the tank pumped while the drain field is flooded: the EPA warns a pumped-out tank can try to float out of saturated ground. A drain field repair or replacement usually needs a permit in Florida. See drain field repair.

6. Bright green, lush grass over the tank or drain field

The EPA lists bright green, spongy, lush grass over the septic tank or drain field, even during dry weather, as a warning sign.

What to do: Note whether the green strip stays green in a dry spell and whether the ground there is soft. Mention both when you call. Together with wet spots, it may point toward the drain field.

7. A septic alarm going off

Systems with a pump chamber, such as many mound systems, have a high-water alarm, and an EPA fact sheet says most aerobic treatment units (ATUs) come with an alarm and control system to detect mechanical breakdown. A Washington State Department of Health guide to mound systems explains that a float in the pump chamber triggers a light and buzzer when the liquid level gets too high. The cause could be a faulty pump, float or circuit, or too much water use.

What to do: The same guide advises conserving water (no baths, showers or laundry) so the reserve space in the pump chamber buys time. Call your septic company. Don't handle the pump, floats or wiring yourself: the guide says to turn off the power at the circuit breaker and unplug all power cords before anyone handles the pump or floats, and that service or repair of pumps and other electrical equipment must be done by a licensed professional. Do not enter the pump chamber: the guide warns the gases inside are poisonous and the lack of oxygen can be fatal. If you have an ATU, call the maintenance company on your service contract. Florida law requires an ATU owner to keep a maintenance agreement with a permitted maintenance entity that inspects the unit at least twice a year. (The owner of an owner-occupied home can be approved as the maintenance entity for their own unit after training certified by the manufacturer's representative.)

Signs you cannot see from the yard

The EPA also lists signs that show up away from the house: algae blooms in nearby lakes or ponds, and high levels of nitrates or coliform bacteria in drinking water wells or surface water. If you think your well water may be contaminated, the EPA suggests checking with your local health department about having it tested.

Safety first

Sewage in the house or on the ground is a health risk. The EPA says to avoid contact with it, because it may contain harmful germs, and the CDC advises keeping children and pets away from the affected area. Keep people and pets away and call a septic company. If anyone is hurt, or has fallen into or collapsed near a tank, call 911. If the ground over the tank is settling or sinking, keep people off it: the EPA lists settling as a sign of a damaged tank after flooding. For cleanup and safety steps, read sewage backing up into the house.

What it may cost

If the tank just needs pumping, national cost guides put a routine pump-out at $290–$600. A typical septic repair runs about $600–$3,000, drain field repairs about $1,000–$5,000, and replacing a conventional drain field about $3,000–$15,000. Florida's septic rule does not count routine pumping as a repair (Rule 62-6.002), so it does not need a repair permit, but most repairs do. Local rules can differ, so ask your county permit office. The Florida septic pumping cost guide has the details.

How to prevent these problems

Pump and inspect on schedule. The EPA says to inspect at least every 3 years and pump typically every 3 to 5 years. The pumping interval calculator gives an estimate for your household.
Spread out water use. Run full loads of laundry and spread them over the week.
Flush only human waste and toilet paper. Wipes, grease, paper towels, coffee grounds and chemicals cause trouble.
Protect the drain field. Do not park or drive on it, keep trees at a distance, and send roof drains and other rainwater away from it.
Skip the additives. The EPA does not recommend them, and a Washington State Department of Health guide says they do not reduce the need for routine pumping.

To find a company, browse the directory or start with Tampa, Orlando, Ocala, Brandon and Kissimmee. Our guide to what happens during a pump-out explains the visit.

Frequently asked questions

How do I know if my septic tank is full?

You usually cannot tell from inside the house until problems start. The reliable way is to have a professional measure the sludge and scum layers. The EPA says a tank should be pumped when the bottom of the scum is within 6 inches of the outlet, the top of the sludge is within 12 inches of the outlet, or the two together fill more than 25% of the tank's liquid depth.

Can a full septic tank fix itself?

No. Sludge and scum only build up. Bacteria break down some of the waste, but pumping is what removes the solids.

Will pumping fix a failing drain field?

Pumping removes solids from the tank, but it may not by itself fix a drain field that is no longer taking water. A septic professional can tell you whether the field needs repair.

Does heavy rain cause septic problems?

It can. A drain field needs unsaturated soil, and the EPA says a flooded drain field can send sewage to the surface or back up into the house. If problems show up only after heavy rain, cut water use until the ground dries, and do not pump the tank while the drain field is flooded.

Who do I call?

A septic company first. For a sewage backup into the home, the EPA also suggests your local health department. Check that the company is registered with Florida DEP using our registration checker.