5 Types of Septic Tanks

By: First Supply

Modern plumbing plays a huge part in making our lives more comfortable and preventing the spread of disease. Plumbing systems deliver a reliable source of clean drinking water and remove sewage and wastewater. There are two ways to drain wastewater from residential and commercial buildings. Structures will either be tied into municipal sewer lines or use a septic system. The key difference between the two is that a septic system serves an individual property, while sewer lines connect multiple properties into a network of pipes that carry waste to a municipal wastewater treatment facility. Sewer lines are more common in urban areas and septic tanks are more likely to be found outside city limits on rural properties.

Parts of a Septic System

Two main components are required to make a septic system work – a septic tank and a drainfield. A septic tank is a watertight box with inlet and outlet pipes. Wastewater flows into a septic tank and remains there long enough for solids and liquids to separate into three layers.

Layer #1
The top layer is formed when solids lighter than water (like oil and grease) float to the top to create a layer of scum.

Layer #2
The middle layer includes partially clarified wastewater.

Layer #3
The bottom layer is created when solids heavier than water settle on the bottom of the tank to form a layer of sludge.

The scum (top) layer and sludge (bottom) layer remain in the tank where naturally occurring bacteria break them down as much as possible. Solids that can’t be broken down any further stay in the tank until the tank is pumped out thereby reducing the amount of space available in the tank. A layer of clarified liquid is sandwiched between the sludge and scum layers. This liquid leaves the tank and travels into the drainfield (also known as a soil absorption field) where it’s filtered through gravel and soil.

Septic System Advantages

There are many reasons that people may prefer a septic system. Since septic systems treat and dispose of household waste water onsite, they are a more economical solution in rural areas where properties tend to be larger and houses are set farther apart. Septic systems don’t require the installation of miles of sewer lines, which makes them less expensive to install. On the other hand, septic systems do require maintenance and a commitment to proper use. If there is a choice available, and sometimes there isn’t, a person should consider whether they’d rather have the ease of use and extra cost of sewer lines, or the extra responsibility of septic system maintenance and lower overall cost.

Septic Tank Types

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.

Concrete

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.

Steel

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.

Fiberglass

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.

Plastic

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.

Aerobic

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.

A Clear Choice?

Unfortunately, there isn’t a one-size-fits-all septic tank option. The best type of septic tank for one situation might not be the best for another. The advantages and disadvantages listed in this article should help anyone considering septic systems make an informed choice. First Supply is your best source for reliable information, tools and supplies.

FAQs: Types of Septic Tanks & Septic System Basics