The septic tank is part of your home wastewater treatment system. Wastewater flows into the tank where microbes begin to break down the waste. Oils and grease float to the top as a layer of scum, while solid waste sinks to the bottom as a layer of sludge.

Effluent then flows from the tank through piping to an absorption field or leach field. Proper septic system maintenance reduces the risk of contamination to nearby drinking water wells and other bodies of water. For more information, click the link provided to proceed.

A septic tank is a large, watertight container that receives all wastewater from your home. After entering the tank, waste separates into three layers: sludge, scum, and liquid effluent. A healthy population of anaerobic bacteria in the tank breaks down organic waste and prevents it from overflowing or contaminating the drain field. A baffle on the top of the tank keeps scum from floating to the surface and clogging inlets and outlets.

A septic tank baffle is a round or rectangular piece of concrete, fiberglass, polymer, or steel that separates the sludge and scum layers inside your septic tank. The baffle is attached to the inlet pipe and the outlet pipe. It is also connected to a T-shaped outlet that opens above the scum layer. This ensures that all of the sludge and scum stays in your tank instead of traveling to the absorption field, where it would clog and damage the soil.

The liquid effluent is the remaining liquid and semi-buoyant waste particles that are not broken down by anaerobic bacteria in the septic tank. It is pumped out of the tank through a T-shaped opening into a distribution box and then into your drainfield. It seeps through perforated pipes into the soil underneath, where it filters through rocks, dirt, and sand to remove impurities naturally.

Bacteria generate gases as they break down wastewater contaminants. These gases, including hydrogen sulfide, can build up and create pressure that can block the septic tank inlet or cause sewage to back up into the house. A vent in the septic tank lid opens when hydraulic pressure builds up to release these gases through a mushroom-shaped cap that can be fitted with a charcoal filter to reduce odors.

A septic tank must be correctly sized to accommodate the number of people living in your home and the amount of wastewater it produces daily. A poorly sized septic system can cause overflow and backups, which can lead to contamination of soil and freshwater sources. In addition, homeowners should not flush chemicals or materials that may disrupt septic tank and absorption field operations. These include commercial and household bleach, disinfectants, solvents, floor cleaners, sink cleaners, motor oil, antifreeze, photo chemicals, or other harmful substances. Other items that should not be flushed include paper towels, cotton swabs, toilet paper, dental floss, cigarette butts, plastics, and bones.


Septic sludge is the solid waste that accumulates in a septic tank. It is created when gray wastewater (from kitchens or laundry rooms) and black wastewater (from toilets) are drained into the tank. As the wastewater settles in the tank, it separates into three layers: scum, effluent, and sludge. Scum is the top layer of the water, which consists of oils and fats that float to the surface. It is often comprised of soaps and greases that result from washing dishes, cleaning products, and washing hands. The middle layer is the wastewater, which contains waste particles and liquids. The bottom layer is the sludge, which consists of heavier waste solids that sink to the bottom. The sludge is decomposed by bacteria in the tank. It can take up to 24 hours for the bacteria to fully break down the sludge.

If a septic system is not properly maintained, the sludge may start to build up in the septic tank. This can clog the inlet and outlet tees, which will prevent wastewater from entering or exiting the tank. It can also clog the soakaway, which is a network of pipes that carry pre-processed sewage into the soils surrounding the septic tank.

Proper septic tank maintenance includes regularly monitoring and pumping the tank. Keeping the septic tank at or below 30% sludge is ideal. A septic tank that is over 30% sludge can cause septic tank leaks, clogged drains, and raw sewage backups in the home.

It is also important to know what not to flush, and to make sure that septic tanks are large enough to manage household waste. Typical items not to flush include paper towels, cotton swabs, dental floss, sanitary products, coffee grounds, pet feces, cigarette butts, and other waste that does not easily degrade. It is also important to never add commercial septic tank additives to the septic tank, as they can disrupt natural bacterial processes and the septic system.

With regular septic tank pump outs, proper septic tank maintenance, and the use of a biological digester such as Muck Munchers, you can minimize the risk of a septic tank sludge build-up. This can help to protect your septic tank and your home from costly repairs, replacements, or septic tank leaks.


As wastewater from your toilets, showers, bathtub, sinks, and washers drains into your septic tank, it undergoes a settling process. Solid materials like fats, oils, and soaps float to the top of your wastewater (scum), while debris, including paper and plastic wastes, sinks to the bottom of the tank, becoming sludge. Anaerobic bacteria in your septic tank then eat away at the sludge and turn it into liquid effluent.

When you flush your toilets or run water in your home, hydraulic pressure pushes the liquid waste out of your septic tank through the outlet tee into your septic system’s drain field. This forces the wastewater through a filter before it enters soil for further treatment. If scum or sludge is allowed to make its way to your drain field, it can clog the septic system and prevent wastewater from being properly absorbed by the soil.

A septic tank’s inlet and outlet tees are designed to prevent scum and sludge from entering the outlet tee and leaving your septic system. The inlet tee is usually elevated above the tank bottom and has a narrow vertical section that extends into the water. The top of this section is several inches above the bottom of the scum layer in the tank. The outlet tee is also designed with baffles to prevent scum and sludge.

Septic tanks are typically made from concrete, fiberglass, or polyethylene because these materials are sturdy and not prone to cracking while underground. If a septic tank cracks, waste will leak out and form puddles around the septic system’s drain field.

You can avoid problems with your septic tank and drain field by periodically checking the sludge level in your septic tank. If the sludge layer rises above the top of your tank’s inlet tee opening, you may need to add a bacterial additive or pump out your septic tank. If the tee is clogged, a professional can use a high-pressure pump to force water out of your tank. Adding the additive to your septic tank helps reduce odor and bacteria, as well as help break down solids in the septic system.

Absorption Field

When your septic tank is full, wastewater leaves through a pipe into an absorption field (also called a drain field or leach field). This is a series of underground gravel trenches that allow the wastewater to leak out and seep into the soil below. The soil functions as a filtration system and further treats the wastewater, reducing levels of harmful bacteria and other contaminants.

Sludge is a buoyant waste that floats on top of the liquid effluent in your septic tank. The inlet and outlet tees in your tank are designed to keep this sludge from exiting the septic system through these pipes, but if you don’t pump your septic tank regularly, this sludge can accumulate and clog your inlet and outlet tees as well as the pipes from the inlet and outlet. Sludge also may clog the drain field, preventing it from treating your wastewater properly and polluting groundwater.

Effluent that reaches the absorption field passes through a distribution box to ensure that the wastewater is evenly distributed over your drain field or fields. The distribution box may include multiple outlets or a series of parallel pipes that connect to each section of the drain field.

If the distribution box isn’t working as it should, it may be necessary to install a sump pump to remove the wastewater from the septic system to the drain field during heavy usage. You should never try to use a septic tank without a functioning distribution box and absorption field.

The size of your absorption field depends on the percolation rate of your soil. A percolation test is conducted by a licensed inspector who can recommend the correct size for your drain field. The rate is based on the amount of sand, silt and clay in your soil. Generally, a sandy soil has a higher percolation rate than a clay soil.

A seasonal high water table during rainy periods can saturate the soil, reducing its ability to accept wastewater from your house. Possible solutions to this problem include installing interceptor drains, lowering the water table with a lift pump or modifying your absorption field.

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