Septic tank plumbing 101: How do septic tanks work?


By Kristy Snyder

Septic tanks aren't exactly glamorous, but they're important for keeping waste from piling up inside your home. Ever wondered how that mysterious underground system handles all our waste? Well, you're in the right place. 

As a homeowner, understanding the basics of septic tank plumbing is essential for maintaining a healthy and functional system. In this comprehensive guide, we'll explore what a septic tank is, how a septic tank works, the various types available, maintenance tips, common repairs, and the professionals you should contact when issues arise.

What is a septic tank?

A septic tank is a large underground container that collects and processes sewage from the household. Its purpose is to help waste decompose so that it can be filtered back into the soil. Typically, all of the water that goes down a drain in your home will flow through a main drainage pipe into your septic tank.

It consists of two main chambers: one for solid waste to settle and another for liquid effluent to flow out into the drain field. Usually, it's set up somewhere in your backyard, away from your house.

A septic tank is a way for you to treat your home's wastewater when you don't have access to a sewer line. They're especially popular in rural areas where there are no public sewer systems set up.

How does a septic tank work?

septic tanks in groundBefore we explain how a septic system works, you need to understand its two main parts: a septic tank and a drain field.

The septic tank, as we've mentioned, is where all of your solid and liquid wastewater goes after flowing through the drainage pipe. But the drain field is where liquid waste from the tank — better known as effluent — eventually drains out into the soil. It's a shallow, excavated area of your yard that's covered up. You might also hear the drain field referred to as a "leach field."

Now that you have the basic terms down, here's a step-by-step guide on how a conventional septic tank system works:

1. Wastewater flows from your home. Any time you flush a toilet, take a shower, or wash your dishes, that water collects into a single drainage pipe to flow out of the home. This drainage pipe carries the waste directly into the septic tank.

2. Liquids and solids begin to separate. Inside the tank, the heavy lifting begins. The solids in the wastewater, like toilet paper and other organic materials, sink to the bottom. Within 24 to 48 hours, this becomes a sludge layer that bacteria in the tank can feast on.

Meanwhile, any oils or grease floats to the top of the tank. These won't be released into the drain field yet. A T-shaped outlet, along with a second compartment, prevents any of this unprocessed gunk from leaving the tank prematurely. However, it does allow any water or other liquid waste to pass through.

3. Bacteria break down solids. Bacteria in the septic tank go to town on the sludge layer, breaking down the solids into gasses and effluent. Effluent rises to the top of the tank and eventually makes it into the next compartment.

4. Effluent exits the tank. The effluent leaves through an outlet pipe and flows into the drain field. The soil in the drain field continues to filter and treat the wastewater, eventually converting it into normal groundwater.

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Are there different types of septic tanks?

Yes, there are several types of septic tank systems. The one we discussed above is called a conventional septic system, and it's what most people have.

Here are a few of the other common septic systems:

  • Aerobic treatment unit. Unlike traditional anaerobic systems, aerobic treatment units use oxygen to enhance the breakdown of solids, providing a higher level of treatment. They're particularly beneficial in areas with high groundwater tables or poor soil conditions.
  • Chamber septic system. Chamber systems replace traditional gravel-filled trenches in the drain field. These chambers help effluent better infiltrate into the surrounding soil, improving effluent distribution and absorption.
  • Drip distribution septic system. This system utilizes a long network of pipes with small drip holes to evenly distribute effluent over a large area in the drain field. It's great for sites with limited space.
  • Evapotranspiration septic system. Evapotranspiration systems treat water and then release it into a shallow bed of gravel or soil, promoting water uptake by plants and evaporation into the atmosphere. These systems work best in areas that get a ton of heat and sunlight.
  • Mound septic system. With a mound system, effluent is pumped into a mound made of sand and gravel, allowing for enhanced treatment before percolating into the soil. Mound systems are good in situations where you don't have enough room or the right soil for a traditional drain field.
  • Recirculating sand filter system. These systems use sand filters to further treat effluent before recirculating it through the system, achieving enhanced treatment. They're ideal when dealing with challenging soil conditions.

How to care for your septic tank.

professional cleaning and unblocking septic tank systemSeptic system maintenance is crucial. If you neglect to maintain it, it could back up and lead to a nasty overflow.

The Environmental Protection Agency (EPA) says your septic system should be inspected at least every three years by a qualified professional. During this septic tank inspection, a professional will make sure the septic tank is functioning well. They will also likely perform septic tank pumping, which is when the sludge and scum are removed from your tank.

According to the EPA, septic tanks typically need to be pumped in these three instances:

  1. When the scum layer is within 6 inches of the bottom of the outlet.
  2. When the top of the sludge layer is within 12 inches of the outlet.
  3. When more than 25% of the liquid depth is sludge and scum.

Of course, you can do plenty of other things to ensure your septic tank runs smoothly in between service provider visits. Consider the following tips for caring for your septic tank:

  • Switch to a high-efficiency toilet, faucet aerators, and showerhead. This will reduce the amount of water your septic tank has to process.
  • Don't throw waste down the toilet. Don't throw things like diapers, feminine hygiene products, paper towels, or any other non-biodegradable trash into your toilet. These will just clog up your system.
  • Avoid dumping chemicals down the drain. Your septic tank has a delicate balance of bacteria that work to break down waste. You might kill them if you dump toxic liquids in your sink.
  • Keep your drain field clear. Make sure trees and other large-root plants don't start growing in it. Also, make sure the area isn't getting flooded with extra water from roof drains, sump pumps, or other drainage systems.
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Who should I hire for my septic tank system?

Septic tanks can be a messy business, so they're not something you want to handle on your own. Luckily, a septic service professional will know all of the tips and tricks to keep your system running smoothly. A local plumber may also be able to service your septic system. However, make sure they have the experience and qualifications.

If you need help finding a septic and plumbing specialist in your area, download Thumbtack today. On the app, you can see the best septic tank services in your area and get free cost estimates.


Where should a septic tank be placed?

Place your septic tank away from your house in an area suitable for drainage and easily accessible for pumping trucks. Typically, this is an area with level ground not prone to flooding or surface water ponding.

Also, make sure your septic tank is easy to access. Don't place it under massive tree roots or rocks.

Most local health departments or municipalities have specific requirements on how to place a septic tank. When in doubt, you can always ask a local pro where you should have your tank installed.

How does a septic tank drain?

Treated liquid flows out through an outlet pipe to the drain field, where it seeps into the soil for further purification. No fancy mechanics involved.

What are some signs of septic system failure?

Slow drains, gurgling sounds in pipes, standing water near the drain field, and unpleasant odors are all red flags your septic system might be failing. If you experience those, get in touch with a septic pro ASAP.

How do you tell if your septic tank is full or clogged?

The signs of a septic tank being full are similar to the signs it's failing. You might notice your toilets and drains won't flush. You might also find your lawn flooded or smelling like raw sewage.

Does my sink drain into my septic tank?

Yes, most household sinks should drain into your septic tank. This means all the water you use to brush your teeth, wash dishes, and rinse off your vegetables goes to the same place as your toilet wastewater.

What pipes are connected to a septic tank?

Typically, there is one main drainage pipe connected to a septic tank along with one or more discharge pipes. The main drainage pipe is what carries all of the wastewater from your home into the septic tank. Once the waste is processed, it exits the tank through one or more perforated pipes in the drain field.

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