Septic Tank: Types and How Septic Tank Work!

What is a Septic Tank?

A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (sewage) flows for basic treatment. Settling and anaerobic processes reduce solids and organics, but the treatment efficiency is only moderate.

Septic tank systems are a type of simple onsite sewage facility (OSSF). They can be used in areas that are not connected to a sewerage system, such as rural areas.

The treated liquid effluent is commonly disposed of in a septic drain field, which provides the further treatment. Nonetheless, groundwater pollution may occur and can be a problem.

The term “septic” refers to the anaerobic bacterial environment that develops in the tank that decomposes or mineralizes the waste discharged into the tank. Septic tanks can be coupled with other onsite wastewater treatment units such as biofilters or aerobic systems involving artificially forced aeration.

The rate of accumulation of sludge also called septage or fecal sludge is faster than the rate of decomposition. Therefore, the accumulated fecal sludge must be periodically removed, which is commonly done with a vacuum truck.

Septic Tank Construction

A septic tank consists of one or more concrete or plastic tanks of between 4000 and 7500 liters (1,000 and 2,000 gallons); one end is connected to an inlet wastewater pipe and the other to a septic drain field.

Generally, these pipe connections are made with a T pipe, allowing liquid to enter and exit without disturbing any crust on the surface. Today, the design of the tank usually incorporates two chambers, each equipped with an access opening and cover, and separated by a dividing wall with openings located about midway between the floor and roof of the tank.

Wastewater enters the first chamber of the tank, allowing solids to settle and scum to float. The settled solids are anaerobically digested, reducing the volume of solids. The liquid component flows through the dividing wall into the second chamber, where further settlement takes place.

The excess liquid, now in a relatively clear condition, then drains from the outlet into the septic drain field, also referred to as a leach field, drain field, or seepage field, depending upon locality. A percolation test is required prior to installation to ensure the porosity of the soil is adequate to serve as a drain field.

The remaining impurities are trapped and eliminated in the soil, with the excess water eliminated through percolation into the soil, evaporation, and by uptake through the root system of plants and eventual transpiration or entering groundwater or surface water.

A piping network, often laid in a stone-filled trench (see weeping tile), distributes the wastewater throughout the field with multiple drainage holes in the network. The size of the drain field is proportional to the volume of wastewater and inversely proportional to the porosity of the drainage field.

The entire septic system can operate by gravity alone or, where topographic considerations require, with the inclusion of a lift pump. Certain septic tank designs include siphons or other devices to increase the volume and velocity of outflow to the drainage field.

This help to fill the drainage pipe more evenly and extend the drainage field life by preventing premature clogging or bio-clogging.

An Imhoff tank is a two-stage septic system where the sludge is digested in a separate tank. This avoids mixing digested sludge with incoming sewage. Also, some septic tank designs have a second stage where the effluent from the anaerobic first stage is aerated before it drains into the seepage field.

A properly designed and normally operating septic system is odor-free. Besides periodic inspection and emptying, a septic tank should last for decades with minimal maintenance, with concrete, fiberglass, or plastic tanks lasting about 50 years.

Septic tank diagram

Waste from your house settles into three layers. The septic filter keeps the drain field pipes from clogging.

septic tank diagram

Types of Septic Tank

Septic tanks made of different materials offer varying levels of strength and durability. Here’s a list of pros and cons for the most common types of septic tanks.

1. Concrete septic tanks.

These durable tanks will usually last for several decades. Although, if the concrete cracks this type of tank can let waste seep out and allow groundwater to seep inside. When backups occur in a concrete septic tank, the blockage could impact the outflow of water.

2. Steel septic tanks.

While steel is an inherently durable material, septic tanks made of steel usually only last 25 years before they begin to rust. For this reason, steel septic tanks are less likely to be chosen by homeowners.

When corrosion starts on the roof of a steel tank, the tank could become too weak to support the weight of the ground above it. If this happens, an animal or person could fall into the tank.

To save money, the cover of a steel tank could be replaced if the rest of the unit is structurally sound. Property owners should watch for rust formation on entry and exit baffles.

3. Fiberglass septic tanks.

Septic tanks made of fiberglass won’t crack like concrete or rust like steel. Fiberglass tanks are also significantly lighter than tanks made of other materials – this makes them easier to install but also means they are more likely to shift when the surrounding soil becomes saturated.

4. Plastic septic tanks.

Plastic tanks are durable, lightweight, and relatively inexpensive. Plastic septic tanks won’t rust and are less susceptible to cracking compared to concrete. These tanks are very light which makes them easy to install.

However, they are so light that they are prone to damage during installation. In addition, plastic tanks can float to the surface if they aren’t installed correctly.

5. Aerobic septic tanks.

These tanks are powered by electricity and are often installed when other tanks on a property have failed.

Aerobic tanks are up to three times more expensive than other types of septic tanks, but they are more effective and require smaller drain fields which can be a huge benefit on smaller properties. These tanks require more frequent maintenance, but they generally last for many years.

Read More: Aerobic Septic System: Types, Cost, and Working

How does a septic tank work?

The septic tank is a buried, water-tight container usually made of concrete, fiberglass, or polyethylene. Its job is to hold the wastewater long enough to allow solids to settle down to the bottom forming sludge, while the oil and grease float to the top as scum.

Regular ‘pumping’ removes sludge and scum from the tank, helping to keep a septic system in top shape.

A well-designed, properly installed septic system can last for decades or fail in just a few years. It’s up to you as long as you can answer how do septic systems tanks work.

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 works.

Good maintenance starts with understanding how does a septic system work 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, I’ll show you why things go wrong and give you some pointers for keeping your system in top shape.

Understand that a septic system is a cafeteria for bacteria

Bacteria are what make a septic system work. They break down waste, leaving the 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. A layer of scum floats to the top. Scum is primarily composed of fats, greases and oils. The septic tank acts like a settling pond. Greases and oils float to the top. Heavier solids sink to the bottom.
  5. A 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 the decomposition of the waste.
  9. Clean water seeps down into the groundwater and aquifer.

Septic Tank Clean Out

A septic system that was properly designed and installed needs only occasional ‘pumping’ to remove the sludge and scum from the tank. But without knowing how does a septic tank works, you can do things that harm or destroy the system.

  • Waste that decomposes slowly (or not at all) gets flushed down drains. Cigarette butts, diapers, and coffee grounds often cause problems.
  • If used heavily, garbage disposers 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.

How Often Should a Septic Tank be Pumped?

Because every septic tank is custom-sized based on the home and local codes, it’s hard to generalize how quickly a given septic tank needs to be pumped.

However, it is best practice to have sewage professionals inspect your septic tank every three years or sooner and have it pumped every five years or less, depending on the size, the number of people in the home, and their habits.

If you just purchased a home with a septic system, have it inspected right away by a professional?

Read More: Septic Tank Pumping: Ultimate Homeowner’s Guide

How Much Does It Cost to Pump a Septic Tank?

Based on the national and regional averages, a homeowner can expect to spend anywhere between $200 – $600 every time the septic tank is pumped, though this depends on the company, size of the tank, and other factors.

To put this into perspective, if you pump your septic tank every five years and the cost was $300, you only paid $60 per year to manage your sewage, which is less than the cost of sewage management when living in average apartment.

How big your septic tank is will affect the cost of cleaning. It costs an average of about $0.30 per gallon to pump a septic tank, and most septic tanks range somewhere between 600 and 2,000 gallons in size.

The size of your septic tank will also affect how long you can go between cleanings because larger septic tanks don’t need to be pumped as often as smaller models.

Most tanks rely on gravity to work. Wastewater flows into the tank, which is buried in the ground outside your home, and water in turn is carried from the tank to a drainage field using sloped pipes.

Signs Your Septic Tank is Getting Full

Homeowners often worry about when the septic tank will be full, and rightly so. If you wait too long or ignore the signs, your sign may come as the worst and most obvious one: a sewage backup. Some other signs your tank is close to full are outlined below:

  • Strong odors coming up in drain pipes like the sink, dishwasher, or laundry machine
  • Chronic slow draining of pipes after troubleshooting and attempted fixes
  • Water pooling around the septic tank site in your yard
  • Luscious green grass near septic tank site (healthier than normal grass)

Homeowner Tip: In periods of heavy rain, the septic can actually fill up at times, and it may seem like you have an issue, but really the water just needs to go down over time.

How Are Septic Tanks Pumped?

When you hire a company to pump your septic tank, they will likely come with a large truck with a giant tank. Attached to this truck is a giant suction hose that literally sucks up the waste from your septic tank once it is opened.

That sewage is pumped out and stored in their truck and transported to a sewage processing site and safely handled.

Read More: Septic Tank Pumping: Ultimate Homeowner’s Guide

How to Maintain a Septic Tank

When regularly maintained and serviced, a septic tank can last forty years or more and run smoothly without issue. However, if you don’t maintain it, eventually, you could experience backups of sewage in the home, above ground, or in groundwater supplies, which is a dangerous and costly expense to fix.

In most cases, after the harmful sewage is removed, you’ll need to replace the entire septic tank, a cost that can soar above $10,000.

There are septic tank treatment materials that can be flushed down toilets to help break down the material in your septic tank as well, such as Rid-X.

Be sure to read the labels on all products to make sure you understand how they work and possible complications for incorrect use prior to purchasing. When in doubt, talk to your plumber about what product they recommend for routine maintenance and how to use it.

Important to remember: with a septic tank system, everything that is discharged down your toilet, shower, sinks, laundry machine, dishwasher, and garbage disposal enters the septic tank, so take caution and be aware of what is sent down your drains.

Pro-Tip: Contrary to popular opinion, if you own rental properties or are worried about solid items being flushed down your drains or toilet.

We still do not recommend getting a grinder pump because they shred everything up into such a fine slurry, solids are unable to be separated from liquids and are passed through the secondary system (a bad thing). But, be sure to consult with a professional plumber for specific advice on your application.

Read More: How to Clean and Maintain Your Septic Tank?

Important Maintenance Tips for Your Septic Tank

  • Have the tank inspected and pumped regularly, every few years
  • Avoid overusing water (septic tanks can fill up or overflow with greywater while being filtered)
  • Use high-efficiency toilets, faucets, showerheads, and appliances, like dishwashers and laundry machines
  • Do not flush anything down the toilet except human waste and toilet paper. Consider using child locks on toilets
  • Avoid draining excessive chemicals and cooking oils in sinks (they kill organisms in the tank that break down the waste)
  • Limit or don’t use chemical pipe & drain cleaners

How to Clean a Septic Tank Naturally

Some people prefer to maintain their septic tanks with a more hands-on, natural approach. Using a mixture of baking soda, vinegar, and lemon is less harmful than pouring harsh chemical cleaners like bleach down your pipes, and won’t kill all the natural bacteria that are critical to breaking down the waste in your tank.