What are septic tanks and how do they work? Complete overview

A septic tank is a system used to treat wastewater and sewage in rural areas, usually from a home or business. A septic tank can be a simple installation, or it may require professional engineering and construction. 

An organic process in the tank breaks down the sewage and converts it into smaller parts. This can eventually be used in the drain field to fertilize it. From time to time the tank has to be inspected to see if it is working correctly. Every 3-5 years it might be needed to clean it. This removes everything out of the tank so that the process can restart.


Houses in cities have access to the city sewage system and don’t need a septic tank. This makes it easier as a septic tank can require some maintenance and are quite expensive (up to 50000 USD). Local governments are often very strict and have a lot of rules around septic tanks.

How do septic tanks work?

Septic tanks are made of plastic, fiberglass, or concrete. Plastic is cheaper than concrete but doesn’t last as long. Let’s discuss this in more detail. They come in several sizes, based on the need of the home.

There are 3 types of septic tanks: gravity-based, pressure-based, and systems that don’t have a lot of soil. The type is selected based on the needs and the composition of the soil.

1/Gravity-based system

This system has 3 parts: the tank, a drain field (gravel or graveless: plastic chambers), and the soil around it.

The tank has 2 compartments that are connected with drainpipes. The dirty water enters the first compartement with a drain that comes from your home. This dirty water is called sludge and gets processed by bacteria. This sludge gets converted into a cleaner scum layer that rises to the top of the tank. Once it is there, it can move to the second compartment that contains the cleaner water, also called effluent.

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The drain field spreads out the effluent over the ground so that it gets processed further. This is done by spreading it out over the field by using pipes. A distribution box is used to spread the liquids over the pipes so that the whole field gets covered. There are 2 types of drain fields: gravel-based and gravel-less. The standard systems use gravel so that the effluent doesn’t get in contact with the ground. There are also gravel fewer systems that use plastic parts to spread it out. The last option is often used when the drain field is quite small. 

The drains in the drain field are buried but not that deep. Therefore you have to be careful that you don’t damage them by parking vehicles on it, driving a tractor over it, or riding horses in this field. Also, don’t use garden products in this area that can affect plants. Don’t let rainwater run in your drain field. It is possible to grow plants in it but check which ones are allowed. 

2/ Pressurized system

This type of tank has another part added to the previous system. There is a tank between the first tank and the drain field. This is called the pump tank. A pump has to move the water to the drain field. This is mainly used when the drain field is farther away so that there is enough pressure to get the treated water there. 

This system is more expensive as you need a pump and another tank. You also need electricity for the pump and this can require a lot of maintenance. 

3/ Advanced systems

If there is not a lot of soil available or there is a problem with the composition, other systems such as a  mound system (in which a small hill is created), sand filter, or biofilter can be used to filter the sewage. These systems make sure that it is possible to install a septic tank in a lot of situations, even when there is a small garden or the ground composition is unfavorable. This can really increase the costs though as you need specialized companies to install and maintain them. These systems are more expensive as they might need a pump tank and a pump. They can also require more space.

Systems often have to be inspected and approved. Check what your local rules are by reaching out to the local administration. Sometimes a soil survey is needed before they can let you know what is allowed. Finding the location can require that you hire some experts that survey your land to see where you can position your system without having too many costs.

Standard septic tanks are the most common type. They hold up to 5,000 gallons and can be used for both residential and commercial applications.

Large-capacity septic tanks can hold up to 10,000 gallons and are perfect for larger homes or businesses.

Extra large septic tanks can hold up to 12,000 gallons and are perfect for high-traffic areas such as hospitals or schools.

How to maintain your septic tank

There are a few common problems that can occur with septic tanks:

-The tank may not be able to handle the load

-The tank might not be able to hold enough water

-The tank might not be able to clean properly

-The tank might break down and leak

If they are maintained well, septic tanks can last up to 50 or 60 years. Taking care of your sewage tank is quite simple.

The golden rule is: only water, toilet paper, urine, and feces are allowed in your system.

Don’t flush cat litter, cooking oils, or wet wipes. Don’t use the washing machine more than once per day.  The use of the garbage disposal should also be limited as this can affect the bacteria in your tank and slow the process down. You shouldn’t clean the toilet with bleach either. If you have guests, you might have to educate them on what is allowed to avoid problems. There is no need to add tablets in the tank.

People often want to park cars or trucks on their leach fields. This can damage it though and should be avoided.

The top of the tank has to be easily accessible. You shouldn’t place dirt or soil over it. The tank should be pumped every 2-5 years. We have discussed how to determine if your tank is full here.

You can also clean the filter from time to time. Make sure that you lock the tank afterward. It can also be a great idea to ask someone to help as the gasses from a tank can be overwhelming.

 Check the lid of the tank and inspect for surface standing water on top as this can indicate water leaking into the tank.

The tank can get inspected using cameras. The system often gets pumped empty so that it is possible to see if there are cracks in the bottom. If there is a problem in the drain field, it is possible that holes have to be created in the floor. Specialized equipment is used to do this and this has to happen in the right location so that the drains don’t get damaged. Given that drain fields are quite expensive, it is best to consult a specialized company to see what they recommend. Inspectors are often certified by the state. 

The lid of the tank has to be locked. You also shouldn’t bury the lid of the tank or the monitoring ports.

You can save some money by not installing a riser. We have discussed this part of the tank HERE.