How a Septic Tank Works

All wastewater from your toilets, showers, tubs, sinks and washing machines runs into the septic tank. Solid waste sinks to the bottom and forms sludge, while fats and oils float to the top and form scum. Liquid wastewater (effluent) passes through a filter at the tank outlet.

This prevents solids from entering the absorption field and clogging it. The clarified liquid wastewater then exits the septic tank into the drain field. For more information, click the Septic Tank Armadale to proceed.

Maintaining A Septic Tank: A How-To Guide – Forbes Home

The waste from your home drains into a septic tank through a main pipe known as the inlet. Ideally, this pipe should be constructed of plastic rather than cast iron, which can react with soap and cause clogs. The inlet pipe should be elevated above the bottom of the septic tank to prevent the house sewer line from entering the septic system, which can cause wastewater to back up into your home. The septic tank may also have an inlet baffle, which directs the flow of wastewater into the septic tank and keeps a scum layer from disturbing the sludge below. If a septic tank is missing an inlet baffle, it should be replaced.

Once the septic tank is full of solids, wastewater travels to the outlet pipe. As it leaves the septic tank, this pipe needs to be free of scum and debris. It’s important that this pipe has a sufficiently long outlet baffle to allow the wastewater to rise through it. Otherwise, the sludge layer will block the absorption field and prevent it from processing the wastewater correctly.

A septic tank’s inlet and outlet piping should be constructed of acid-resistant concrete or fiberglass and fitted with sanitary tees. These fittings are usually made of PVC. These pipes should be inspected for damage and corrosion. They should be watertight and capped when not in use. Six-inch diameter inspection pipes should be positioned above the baffles and extend to the ground surface for checking the condition of the inlet and outlet piping.

The septic tank liquid depth, or D, is the distance from the top of the inlet baffle to the liquid level inside the tank. A septic tank with a D less than 60 inches deep won’t work properly, so the inlet and outlet baffles should be evaluated for adequate space. In most cases, the inlet and outlet baffles should extend two to three times the D of the septic tank. This allows them to store the scum layer, keep it away from the inlet pipe and avoid short-circuiting, which means that some of the sewage flows into the tank instead of out through the drain field.

The first chamber in your septic tank separates wastewater solids to prevent them from entering the soil absorption field. Heavy solids settle out to the sludge layer at the bottom of the tank, and lighter solids, such as fats and oils, rise to the top and form a scum layer. Bacteria digest these pollutants, converting them to gas that escapes and to a liquid that passes to the second chamber.

The second chamber further separates wastewater solids from the liquid sewage that flows to the absorption field. During this phase, the septic tank relies on hydraulic pressure to push wastewater to the drainfield, where the bacterial digestion process continues. If the inlet and outlet pipes aren’t correctly sized, the hydraulic pressure may not be sufficient. A septic system that isn’t sufficiently pressurized can also experience clogs and sludge buildup.

If you notice a foul smell, gurgling in the toilet or slow draining in your home, it could be an indicator of problems with your septic tank. This is usually caused by a buildup of sludge or a clogged inlet baffle. An increase in flies, such as drain flies and midges, could also indicate a septic tank problem, since these bugs lay their eggs in wet organic material.

When the septic tank reaches one-third full of sludge, it is time to get it pumped. If your septic tank isn’t pumped regularly, it could overflow and cause contamination, foul odors and structural damage to your home.

Unlike older seepage pit systems, newer septic tanks are designed to have a riser that’s above ground level. This provides access to the septic tank for pumping, maintenance and inspection without digging up your yard.

A septic tank riser is also more water tight than a concrete lid, which can let ground water enter and overwhelm the septic system. Despite their water-tight construction, the lids and risers of a septic tank should be regularly inspected to ensure they’re not cracked or damaged.

The last piece of a septic tank is the drain field, also known as a leach field. It is an underground array of pipes that treat wastewater from the septic system and eliminate impurities after it leaves your home.

As septic tank waste is processed, heavier solids settle to the bottom of the tank where bacteria break them down into sludge. Lighter solids, like oils and grease, float to the top and form a layer of scum. The scum layer and the sludge layer are separated by hydraulic pressure from the water on top, which is then pumped out of the tank to be disposed of in your septic drain field.

A septic tank has an inlet and outlet baffle to prevent the sludge and scum layers from leaving the tank through the inlet or outlet pipe, and thus contaminating the drain field. In the drain field, a bacterial community that thrives on anaerobic digestion continues the work of filtering and cleansing untreated wastewater before it seeps into soil and groundwater.

Effluent from the septic tank enters the drain field through perforated pipes that run beneath a gravel or stone cover. A distribution box buried underneath the drain field helps evenly distribute effluent to each of the trenches in the absorption field.

Each trench in a septic tank drain field is lined with an engineered mix of sand and washed gravel to filter the wastewater. The soil absorbs residual bacteria and particles from the wastewater, and excess water is eliminated by evaporation or transpiration by grass growing above.

Using household chemicals and flushing anything that doesn’t decompose can disrupt this microbial community, causing the drain field to stop working properly. This may cause wastewater to back up into your home, or it could clog and destroy the piping from the tank to the drain field.

To help keep the microbial community healthy, never pour chemicals into your drain field, or use garbage disposals or washing machines that send large amounts of solid waste to your septic tank. Dispose of hazardous and non-hazardous wastes at a local dump or recycling center rather than flushing them down your toilets. It is also important to keep trees and shrubs away from the drain field, as their roots can clog or damage the piping.

Traditionally, a septic tank is buried underground near the house or building. When people use the toilets, waste travels through the pipes into the tank where it settles and decomposes. The tank must be vented to release the gases that build up, or the smelly septic system will become a health and safety concern. Venting ensures that the septic tank and leach field have proper ventilation, which prevents dangerous problems like leaks and odors.

When a septic tank is empty, it is basically just a large underground container that’s filled with air. However, once the septic tank begins to fill with waste and wastewater, it becomes pressurized. That pressure needs to escape or it could cause the septic system’s plumbing to stop flowing or even rupture the tank itself. A septic tank vent allows the pressurized gasses to escape through a pipe that runs from the top of the septic tank to the air outside the home or building.

If you ever see a white pipe sticking up out of the ground, this is likely the septic tank vent. It looks a bit like a white candy cane, and it is usually located about 12 inches above the ground. The location of the septic tank vent will also indicate the general area where the septic tank’s drain field is situated.

A septic system vent must be sized appropriately for the size of the tank and the amount of waste that will be discharged from it. If the vent is too small, it will restrict the flow of sewage, while a vent that’s too big could allow the septic tank to overflow. A qualified septic expert can inspect the vent and determine its proper size.

Another important component of a septic system is the effluent filter. This cylindrical device is installed in the septic tank outlet baffle, and it traps suspended solids that would otherwise clog the septic system’s drain field. The filter is generally cleaned by a professional septic tank service every time the septic tank is pumped.

Many homeowners attempt to camouflage the septic system vent, which often happens with the septic tank vent itself. However, it’s important that the septic vent is not covered or blocked in any way, as this will cause it to fail and lead to serious problems for the septic system.