Fun With Septic Systems

Septic tanks
Nothing like pumping out a septic tank.

Septic Systems Still Service a Significant Number of Households

Although the majority of US households are connected to municipal sewers there are still a significant number of homes and businesses that use a private septic system. Over the years I’ve encountered many homeowners that know very little or nothing about their septic tank or the plumbing that services the septic system.

Full Septic Tank
You don’t want your septic tank to get this full!

Most homes that utilize septic tanks also use ground water from private wells for their potable water. If you’ve already started connecting the dots congratulations, if you have both a septic system and you use a private well those two systems need to coexist and behave well together. Septic systems used groundwater to remove harmful bacteria and most of that wastewater will again become part of the ground water system you use to drink. It is why septic system design is so important.

How Does a Septic System Work? Septic Tank Basics

The first think to know is that all private septic systems have one common goal, to render sewage harmless and inoffensive. I know I’m a plumber so some pretty odd things get me pumped up but septic fields when designed properly are a marvel. The short version of how a septic system works is that sewage flows into a storage tank and that sewage is eaten by bacteria. The septic tank usually contains some sort of baffling system to slow incoming sewage so that the tank doesn’t continually overflow.

**Sewage – any liquid waste containing human, animal, vegetable or chemical byproducts held in suspension or solution. Sewage can contain both ground or storm water.

We will go into further detail on the different stages of sewage treatment however, the first thing to get familiar with is how septic tanks work. It is literally the engine that makes the septic system function efficiently.

A properly functioning septic tank should have 3 naturally occurring levels:

  • Sludge Level – is the stuff at the bottom of the tank. It the matter that is indigestible or too heavy to float. It’s also what will be pumped out of the tank when septic maintenance is needed.
  • Liquid Level – this is the middle level and it consists of small suspended solids and dissolved substances like soaps and minerals.
  • Scum Level – The magic happens right here. It is the top layer of the septic tank and it consists of solids that are light enough to float i.e. grease, human waste, some paper products, etc. This is where anaerobic bacteria digests, decomposes and liquefies the solids. Anything that can’t be digested falls down to the sludge level.
Septic systems
Different settling levels of a septic tank

**Anaerobic Bacteria – it is bacteria that can live without oxygen. So it can continue to digest organic material free of oxygen.

**Aerobic Bacteria – is bacteria that can only live in the presence of oxygen.

Every time raw sewage leaves the house and enters the septic tank an equal amount of waste liquid or effluent is forced out of the tank and into what is called an absorption field.

Sewage Terms: I know it’s sort of disgusting but there are different terms to describe sewage and they are as follows:

  • Fresh Sewage – It’s the freshest (yummy) and it contains oxygen. The water from fresh sewage has dissolved oxygen present.
  • Stale Sewage – Oxygen is starting to be depleted because it is being used aerobically to digest organic matter. Suspended solids are only partly decomposed at this stage.
  • Septic Sewage – is sewage that is being anaerobically decomposed and occurs inside the septic tank or in the absorption field.

All Of The Different Parts of a Septic System Must Work In Harmony

So how does is all work together? Well is starts with proper septic system design. Here are the most common factors that need to be taken in to account when designing and sizing a septic system.

  1. If you get your water from a private well your septic tank and septic field must take into account it’s location. Most municipal codes regarding septic tank systems will clearly spell out safe distances that need to be maintained between the water supply and the septic system.
  2. How much sewage is being produced? Knowing approximate gallons of sewage being used will dictate the size of the septic tank and leach field.
  3. How much room do you have on the property? Smaller plots of property may need a different type of septic tank or a different type of subsoil absorption system.
  4. What kind of ground do you have? What are the absorption properties of the soil on your land? If the
    Septic systems
    Septic Field vs Water Table

    entire property is clay and rock a suitable area for installation is required.

  5. How deep is your private well. Obviously if you have a shallow well for your potable water the proper placement of the septic system is pretty important to alleviate contamination of your drinking water.
  6. How deep is the building sewer? The depth at which the building sewer is installed determines how deep the septic tank will be installed and that in turn determines how deep the absorption fields will be.
  7. Finally, what are your state or local codes that govern septic system installation?

A residential septic system should be designed to hold the sewage from a residential home for about 24hrs. Obviously the more people that reside in the home the bigger the septic tank should be as evident by how tanks are sized, by the number of bedrooms.

Avoiding Septic System Problems – How To Keep The Harmony?

Septic systems
Nothing like pumping out a septic tank.

In addition to proper sizing and installation practices, septic system maintenance is a huge factor in maintaining proper function. I have personally gone into homes that have huge sewer issues only to find that they have a septic system with a septic tank that has NEVER been pumped out.

Let me explain a bit, your home’s sewage drains into a septic tank, that tank is made to begin the breakdown process of the sewage. The process continues in the leach field. Each time sewage enters the tank some of the material that is heavy or can’t be broken down falls down to the sludge level. If the sludge level continues to rise fresh sewage has less and less time to process in the tank. Eventually the fresh sewage drains to the tank and flows right out into the absorption field. Not only does it become very offensive from an odor perspective but it can be dangerous as well. In addition when your tank is filled and your absorption field is saturated and no longer has the ability to take anymore wastewater the sewage begins to back up into the home.

This is how all of the moving parts work together. If the septic tank is properly maintained, the leach field remains affective thereby allowing your sewer to function correctly for decades.

If you have any more questions or issues regarding your septic system please don’t hesitate to reach out.


  1. With many people using septic systems, it is quite important to know how they work. For starters, I do like how you stated that a septic system works by storing the sewage in a large tank and then is eaten by bacteria. This is also why they smell pretty foul. Even with a simple design, everything has to work with eachother in order for it to work properly. If something happens such as a clog, then you’d have to get the help of a service.

  2. I really appreciate the clear explanation of how a septic system works. The diagram of the settling levels helps me better understand it all. My aunt and uncle had a septic system and I never really understood why they wanted us to take short showers and why they had to have it pumped every so often. Now I can see what had them so concerned!

  3. I didn’t realize that there should be three naturally occurring levels in a septic tank. I’ve been doing a lot of research about septic tanks, maintenance, and upkeep. This site has answered a lot of questions I have. By learning more, I hope to not have any problems with my septic system.

  4. Thanks for the article! I love how you explain certain problems that can go with taking care of a septic tank. Maintenance for a septic tank is definitely critical to keeping the tank in good condition. Once, when I was younger, my parents forgot to take care of the tank and, like you said, it backed up right into our house. It was one of the most disgusting things I have ever experienced. I’m glad you have this article to show people the consequences of not taking care of their tanks.

  5. My sister recently purchased a home with a septic tank. She doesn’t really know how they work and would like some background information to know what’s happening in her backyard. I didn’t realize that anything that floats in the scum level can be digested by anaerobic bacteria, and this liquefies the solids and causes it to fall. I’ll be sure to share this information with my sister.

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