How Do Septic Tanks Work?

Just knowing the ins and outs of a septic system can save you a lot of money in the long run. But how do septic tanks work?

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A well-designed, properly installed septic system can last for decades—with proper care and regular inspections. But in order to make sure your septic system is in good shape, it’s helpful to understand how it works.

Maintaining healthy septic systems isn’t all that expensive, but you could easily spend tens of thousands to dig up and replace a septic system that has totally failed. As the old saying goes, an ounce of prevention is worth a pound of cure. It’s important to learn how does a septic tank work.

Good maintenance starts with understanding the types of septic systems, how a septic system works, and how it can fail. Let’s take a look underground and see what’s supposed to happen in a well-functioning septic system. After that, we’ll show you why things go wrong and give you some pointers for keeping your system in top shape.

What Are the 3 Types of Septic Systems?

Septic systems efficiently treat and dispose of sewage and graywater, making them an integral part of many homes. However, not all septic systems are created equal. In fact, there are three primary types of septic systems, each with its own characteristics and suitability for different environments. Understanding these systems is essential for homeowners looking to install or maintain their septic system.

  1. Conventional Septic Systems: Also known as gravity septic systems, these are the most traditional and widely used type. They consist of a septic tank that collects and separates solids from liquids. Once the wastewater is treated in the tank, the effluent flows by gravity into a drain field, where it’s further treated by the soil. Conventional septic systems are suitable for properties with adequate soil permeability and proper drainage conditions.
  2. Pressure Distribution Septic Systems: These systems are ideal for areas with less-than-ideal soil conditions or uneven terrain. They operate similarly to conventional systems but include a pump to evenly distribute effluent throughout the drain field. This ensures more efficient treatment, making pressure distribution systems a versatile option for properties with challenging landscapes.
  3. Aerobic Treatment Units (ATUs): When soil conditions are poor or insufficient, aerobic treatment units come to the rescue. These systems incorporate an aerobic (oxygen-dependent) treatment process, which is more effective in breaking down sewage compared to the anaerobic process in conventional systems. ATUs use pumps and aerators to enhance bacterial action, making them suitable for properties with high water tables or limited soil absorption capabilities.

How Do Septic Systems Work?

Bacteria are what makes a septic system work. They break down waste, leaving water clean enough to safely percolate down into the earth. The whole system is designed to keep bacteria healthy and busy. Some live in the tank, but most do their work in the drain field.

  1. All waste flows to the septic tank.
  2. Watery waste, called “effluent,” fills most of the tank. Anaerobic bacteria begin breaking down the organic material in the effluent.
  3. A layer of sludge falls to the bottom. Sludge is composed of inorganic solids and the byproducts of bacterial digestion.
  4. The septic tank acts like a settling pond. A layer of scum floats to the top. Scum is primarily composed of fats, greases and oils.Heavier solids sink to the bottom.
  5. An effluent filter prevents most solids from entering the outlet pipe.
  6. Effluent flows to the drain field. The drain septic field provides a large area where bacteria can thrive and treated water can seep into the ground.
  7. Holes in the drain septic field pipe allow effluent to seep into surrounding gravel. Gravel around pipes allows water to flow into soil and oxygen to reach bacteria.
  8. Aerobic bacteria in gravel and soil complete decomposition of the waste.
  9. Clean water seeps down into the groundwater and aquifer.

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Septic Tank Inspections

Simple as a septic system may seem, evaluating its health really requires an expert. We highly recommend looking for a contractor who has received some formal training in the science of septic systems. Some states have adopted certification programs for septic contractors—check with your Secretary of State’s office to see if yours is among them.

Having your septic tank inspected will cost a few hundred dollars, anywhere from $200 to $900. From there, your pro will be able to tell you how often your system should be inspected and how does a septic tank work.

A complete inspection will determine whether your system is up to code (many are not) and the condition of the tank and drain field. A good inspector will also be able to tell you whether your tank is large enough for your household, and the maximum volume of water you can pass through it in a day.

You may be able to improve the performance of your system by adding bacteria with a product such as RID-X. Your pro should be able to tell you if your system will benefit from this treatment as you discover how does a septic tank work. These new septic tank treatment pods also ensure your system runs in tip-top shape.

Septic Tank Pumping

Pumping removes the buildup of sludge and scum, which slows down bacterial action in the tank. Your tank may need pumping each year, but it’s possible to go two or three years between pumpings, depending on the size of your tank and the amount of waste you run through the system. Ask your inspector to make a rough recommendation for how often your tank should be pumped.

Regular inspections and pumping are critical for septic system maintenance. But if you’re not squeamish, you can check the sludge level yourself with a device called The Sludge Judge. Once you’ve determined that your tank is one-third full of sludge, call a contractor to come pump it out.

Clogged Septic Systems

If your septic system becomes clogged and you frequently have to clean the filter, you might be tempted to remove it. Keep it.

Septic tanks work by allowing waste to separate into three layers: solids, effluent and scum. The solids settle to the bottom, where microorganisms decompose them. The scum, composed of waste that’s lighter than water, floats on top. The middle layer of effluent exits the tank and travels through underground perforated pipes into the drainage field. There, gravel and soil act as biological filters to purify the wastewater as it sinks into the ground (see illustration above). Have you heard about grey water systems?

Many states and localities require an effluent filter, so keep it in place. Besides, removing the filter could create a far worse (and expensive) problem. Without the filter, waste particles could pass into the perforated pipes and clog them. It would require extensive digging to clean and unclog the system.

However, your filter should not need semiannual cleaning. Most filters don’t have to be cleaned until the tank is pumped, which is typically every two to five years. Chances are you’re putting filter-clogging materials down your drain, such as grease, fat or food scraps.

Alternatives to a New Drain Field

If an inspection or sewage backup reveals that your septic system’s drainfield is in trouble, the ultimate solution is to replace it. The cost can be huge, however, so it’s worth discussing other options with a contractor.

  • Clean the pipes. A contractor can clear out the drain septic field pipes with a rotary pressure washer. “Jetting” the pipes usually costs a few hundred dollars.
  • Treat the system with chemicals. Ask your contractor about treating your system with a commercial product (not a homemade one) that increases the amount of oxygen in the drain field.
  • Loosen the soil. In states where it’s legal, some contractors can fracture compacted soil around the pipes by injecting high-pressure air in numerous locations around the drain field, a process called “terra-lifting.”

Tips to Prevent Septic Tank Problems

From responsible waste disposal to the impact of household chemicals, practical strategies to maintain a healthy and trouble-free septic system are essential. Understanding how certain habits and factors can affect your septic tank’s functionality is key to preventing costly problems down the road.

  • Don’t flush waste that decomposes slowly down drains. Things like diapers and coffee grounds often cause problems.
  • If used heavily, garbage disposals can send too much solid waste into the system.
  • Lint from synthetic fibers flows from washing machines. Bacteria in the tank and drain septic field can’t break it down.
  • Household chemicals like disinfecting cleaners and antibacterial soaps kill bacteria. Most systems can handle light use of these products, but the less you use them, the better.
  • Too much wastewater over a short period of time flushes out the tank too rapidly.
  • Too much sludge reduces bacteria’s ability to break down waste. Excess sludge can also overflow into the drain field.
  • Sludge or scum plugs holes in the pipe.
  • Roots from trees and shrubs can clog and damage a drain field.
  • Compacted soil and gravel block seepage of effluent and deprive bacteria of oxygen. This is often caused by cars driving or parking on the drain field.