How Often Are Septic Tanks Emptied, and Where Do the Contents Go?

By: Josh Clark & Melanie Radzicki McManus  | 
septic tank
A septic pump truck cleans the scum, sludge and effluent from a septic tank. kozmoat98/Getty Images

In modern homes, drains have a way of remaining innocuous. Unless the toilet's overflowing or the bath spigot is filling the tub with blood, plumbers and exorcists aren't usually on our minds. Thanks to the simple push of a lever, waste remains out of sight and out of mind. Not in this article. We're going to your backyard, to the greenest patch of grass, to dive headlong into your septic system.

More than 60 million Americans have a septic system treating the waste in their homes, and about one-third of all new development uses them. By design, these systems are fairly simple. All drains in the home converge to a single pipe that leads to the septic tank buried outside. When the waste water from your toilet, shower, sinks and washing machine leave your house, it's combined. When it hits the septic tank, however, it begins to separate. The heaviest particulate matter in the waste, called sludge, sinks to the bottom. At the top of the tank, fats, oils and proteins form the floating scum layer. In the middle is the comparatively clear liquid layer called effluent or gray water. Combined, these components are called septage.


Septic systems are designed so that only the effluent is discharged from the tank into the drain field (also called the leach field). This is simply a set of pipes with holes drilled into them that release the effluent below ground (but above the water table). The effluent is degraded enough to be well-filtered by good soil. There's plenty of organic material left in the effluent, though, which acts as fertilizer. This is why the drain field usually boasts the healthiest segment of the yard above it.

Simple as their design may be, septic systems require the homeowner to monitor them before problems arise. Usually, once a problem becomes obvious, it's too late for any simple solution. Fixing big septic problems often requires thousands of dollars worth of parts and labor. Fortunately, a little maintenance can go a long way in avoiding problems. Read on to find out how often a septic tank should be pumped out.


Pumping Your Septic Tank: A Good Idea

septic tank
A plumber lifts the cover of a septic tank. To help prevent clogging and buildup, some companies produce toilet paper that dissolves in water. It's helpful, but you should still have your tank inspected and pumped regularly. Kevin Trimmer/Getty Images

Even if you have a well-functioning septic system, a good drain field and a healthy microbial ecosystem breaking down the septage, the sludge and scum layers in your tank will build up over time. Thus, they should be pumped out periodically — generally when the bottom of the floating scum layer is within 6 inches (15.2 centimeters) of the bottom of the outlet tee or the top of the sunken sludge layer is within 12 inches (30.4 centimeters) of it (septic tanks have an inlet tee, or pipe, that brings wastewater in from the house, and an outlet tee, which, in turn, takes the wastewater out of the tank). Without a well-developed power of extrasensory perception, it's impossible to tell when your waste has reached these levels.

This is why the U.S. Environmental Protection Agency (EPA) recommends that people with a septic tank have their system checked every one to three years. Having your system inspected includes getting your sludge and scum levels measured, checking the system's pipes and mechanisms, and inspecting the drain field to make sure it's percolating the effluent properly. The average septic tank system usually requires pumping every three to five years.


There are some products on the market that are meant to prolong periods between pumping. These products contain chemicals designed to hasten the process of breaking down the sludge in your tank by acting like tiny Pac-Men chomping magic pellets. At the least, products such as these may be superfluous: The additives are simply joining the microbial party already in full swing below your lawn. In the worst case, the chemicals can throw the primordial ecosystem that's developed over time in your septic tank thoroughly out of whack and disrupt the natural enzymes' ability to properly break down the waste sent to it. The EPA recommends that septic tank users play it safe and not substitute these products for regular septic tank inspections and pumping.

Without regular pumping of the septic tank, the system can overflow. Sometimes overflow can lead back to the house, where toilets and drains belch forth what's supposed to be in the septic tank. Overflow can also lead to a sudden deluge of unprocessed waste flooding the drain field. When this happens, water can seep above ground, which leads to a flooded yard and run-off into nearby water bodies like creeks and rivers. Below ground, this flood can cause further damage, tainting groundwater. Together, these intrusions of waste can contaminate the water people use and drink. The waste introduced into the water supply can carry harmful bacteria and diseases like hepatitis.

But even after it's taken from your backyard, your septic tank's contents still pose a hazard. So what happens to it?


Disposing of Septage: From Yuck to Eureka!

septic tank
A typical residential septic tank is usually about 4 feet wide (1 meter) by 8.0 feet (2 meters) long by 6 feet (1.8 meters) tall. Jupiterimages/Getty Images

Wherever there are a lot of people operating their homes' waste systems on septic tanks, you can bet you'll find plenty of local businesses that specialize in removing the scum and sludge that accumulate in the tank over time. This is an important service; if too much sludge builds up, it can lead to overflow, which is bad for everybody.

Generally, commercial septic pumping involves a pump truck removing the sludge, effluent and scum in the tank, then leaving the tank empty and ready to be filled again. Once the waste is removed, there are only so many things that can be done with it. Before federal laws that restrict septic sludge dumping, waste companies could simply bury it in dump sites. As it became clear that sites like these were a health hazard, they were outlawed. These sites remain, though many are in the process of remediation (cleanup).


These days, federal and state laws govern the final destination of the contents of your septic tank. In some cases, the septic contents are taken to waste treatment plants and added to the stew piped in from a municipal sewer system or delivered to independent, for-profit companies specializing in the treatment of septage. Septage may also be dumped in approved landfills. The guidelines concerning septage dumping are strict and sites can be few and far between, however.

Because of the dilemma posed by disposing of your septic tank's contents, septage is often used in another way: to grow your food. Unless there's a "USDA Organic" label on it, it's possible the food on your table was grown using the sludge that used to be in your septic tank as fertilizer.

This use of septage can be a controversial one. Proponents, including many commercial farmers, say it's a win-win situation, since municipalities don't have to worry what to do with the waste, and farmers get cheap fertilizer for their crops. If applied correctly to cropland with good soil and a low water table, the soil should act as a filter in the same way a drain field does in the backyard of a home with a septic tank. It is a contentious subject and the use of biosolids in agriculture continues to come under fire as a potential health and environmental threat. The practice can be seen as an effective way to recycle waste, but there are scientists and health professionals who believe that the use of biosolids in agriculture is dangerous for the nation’s farmland and is creating a number of health risks.

There's another, more cutting-edge way septage is being used these days — generating electricity to power homes. It's long been known that the methane produced as a waste product in the breakdown of sewage could be used to generate electricity. While methane is a simple fuel, it can also be broken down and used to generate electricity using fuel cells located on-site at treatment plants. The electricity produced doesn't combust, so there's little or no pollution generated.


Septic Tank Cleaning FAQs

How often should a septic tank be pumped?
Septic tanks should be pumped at three- to five-year intervals, and inspected by a professional once every three years.
Can I pump my septic tank?
You could incur hefty fines for doing so yourself. Across neighbourhoods and localities, this is usually taken care of by licensed companies.
Do septic tank additives help?
No. Some studies have revealed that chemical and biological additives are in fact, detrimental to septic systems.
How do I know if my septic tank needs cleaning?
If your drains are blocked and there is an unpleasant odor, chances are your septic tank is in need of cleaning. If these signs aren't present, you should still consider going for it if three to five years have gone by since the last pumping.
How expensive is it to clean a septic tank?
On average, this can cost around $375. Pumping out the tank can cost $250 for a 3,000-liter tank, and approximately $1,000 for a 5,000-liter tank.

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More Great Links

  • Metro Vancouver. "Turning Wastewater into Energy." (April 13, 2022)
  • Perkins, Tom. "Questions Remain About Using Treated Sewage on Farms." Jan. 30, 2020 (April 12, 2022)
  • U.S. Environmental Protection Agency. "A Homeowner's Guide to Septic Systems." (April 12, 2022)
  • U.S. Environmental Protection Agency. "Frequent Questions on Septic Systems." (April 12, 2022)
  • U.S. Environmental Protection Agency. "Land Application of Sewage Sludge." December 1994. (April 13, 2022)
  • U.S. Environmental Protection Agency. "Septic Systems Overview." (April 12, 2022)
  • Willow Lake Cogeneration Facility. (April 13, 2022)