Septic System Components



There are several different components to a septic system. The following information is for basic, general knowledge only and refers only to a standard septic system. For specific requirements, please refer to the El Dorado County Ordinance or contact your local Environmental Health Specialist at (530) 621-5300.





Septic Components: Cleanout 

"Cleanouts" are pipes running from a septic system up to ground surface, to facilitate "snaking," jet cleaning and other maintenance and trouble-shooting tasks. Usually this above-ground access pipe is found at the beginning of a septic system - in between the house and the septic tank.

Cleanouts are usually located near the house and can give you a general idea on which side of the house your septic tank is located if you do not have that information. co.gif


Sewage is backing up out of the cleanout.


This usually indicates a blockage somewhere between the house plumbing fixtures and the tank. The tank inlet sanitary "T" could also be blocked with solids, not allowing sewage to flow into the tank.     



Septic Components: Septic Tank

The septic tank is a watertight structure that is the main collection point for human waste by-products. It is at this tank that the solid waste is separated from the liquid waste, andImage of Septic tank layers the biological digestion of the waste matter takes place. A septic tank provides anaerobic treatment - it does a good job of settling out the solids, but not such a good job of removing nutrients and breaking down organic matter. Septic tanks are sized according to the amount of liquid waste they must process - this is based on the number of bedrooms.

Tank Components:


Image of Septic tank Components

Inlet Sanitary "T"

All septic tanks have an opening for the waste to enter the tank and another one for the waste to exit the tank. The entrance is called the inlet. Inside the tank there will be a PVC, "T"-shaped fitting, consisting of a short section of horizontal piping leading into a slightly longer, vertical section of piping that is open on both the top and the bottom.

Outlet Sanitary "T"

All septic tanks have an opening for the waste to exit the tank. The exit is called the outlet. Inside the tank, there will be a PVC "T"-shaped fitting, consisting of a short section of horizontal piping leading into a slightly longer vertical section of piping that is open on both the top and the bottom. The top of the vertical section must extend above the level of the scum layer, and the bottom of the vertical section must extend below the bottom level of the scum layer. The outlet tee is usually several inches below the level of the inlet tee.

Effluent Filter

Excessive discharge of solids to the drain field can cause it to plug and lose efficiency in treatment and dispersal of the normal liquid flow. If the problem persists, the drain field may need to be replaced. Septic tank effluent filters provide a relatively inexpensive means of preventing solids discharge. In new septic installation, effluent filters are required at the outlet of the septic tank, in the outlet sanitary "T", collecting solids that may be discharged from the tank. Solid accumulation in the filter will cause poor performance of the septic tank but creates a problem that is far easier and less expensive to clean and maintain than solids accumulation in the drain field.

Scum Layer

This is buoyant waste made up of greases and soaps. When a septic tank is opened, this is usually the first thing that is seen floating on top. If periodic maintenance is not performed (i.e. pumping the tank), this waste can build up to the point of going above the top of the inlet and outlet tees and clogging the inlet into the tank, as well as possibly clogging the soils in the absorption area. 

Liquid Effluent Layer

The liquid effluent is made up of the remaining liquids and semi-buoyant waste particles after the sludge and scum waste have separated. A normally operating septic tank maintains a constant effluent level at the height of the bottom of the outlet tee opening. Consequently, when new waste enters the tank, the liquid effluent level rises and the effluent is forced out of the tank through the outlet into the distribution box and into the absorption area for dispersement and continued treatment. Septic tank effluent is usually cloudy and contains suspended solids and pathogens, including disease-causing bacteria and viruses. This condition requires more bacterial action for treatment than can occur in the tank alone.

Sludge Layer

The sludge layer consists of the heavier waste solids that separate and settle to the bottom. The sludge layer is where the decomposition process continues by means of bacteriological interaction. These bacteria live and grow without the presence of air in what is called an anaerobic treatment. Although decomposition is a continual process, the breakdown is not complete, which can eventually result in waste residue build-up if not pumped out on a regular basis. This residue can build up to the bottom of the inlet or outlet tee and block flow into and/or out of the tank.

Tank Maintenance

The septic tank removes solids by holding wastewater in the tank, which allows the solids to settle and scum to rise to the top. To accomplish this, wastewater should be held in the tank for at least 24 hours. Up to 50 percent of the solids retained in the tank decompose. The remaining solids accumulate in the tank. Biological and chemical additives are not needed to aid or accelerate decomposition.

As the septic system is used, sludge continues to accumulate in the bottom of the septic tank. Properly designed tanks have enough space for up to three years safe accumulation of sludge. When the sludge level increases beyond this point, sewage has less time to settle properly before leaving the tank. As the sludge level increases, more solids escape into the absorption area. If sludge accumulates too long, no settling occurs before the sewage escapes directly to the soil absorption area. To prevent this, the tank must be pumped periodically. The material pumped out of the tank is known as "septage."

The frequency of pumping depends on several factors:

  • Capacity of septic tank.

  • Flow of wastewater (related to size of household).

  • Volume of solids in wastewater (more solids if garbage disposal is used).

The table below gives the estimated pumping frequencies according to septic tank capacity and household size. The frequencies were calculated to provide a minimum of 24 hours of wastewater retention assuming 50 percent digestion of the retained solids.

Estimate Septic Tank Pumping Frequencies in Years (For Year-Round Residence)   


Septic Tank Pumping Frequency

Tank Size (Gallons) Household Size (Number of People Living in Home)














































































Note: More frequent pumping needed if garbage disposal is used.

It is important to note that the soil absorption field will not fail immediately when a full tank is not pumped. However, the septic tank is no longer protecting the soil absorption field from solids. Continued neglect will result in failure and the soil absorption field may need to be replaced. In some cases, replacement of the absorption area may not be possible due to site limitations. 


Septic Components: Septic Tank Access Lids

In order to make repairs or perform regular maintenance or cleaning/pumping of the tank, access must be provided. There are usually two lids located at the top of the septic tank-one located over the inlet "T" and one located over the outlet "T" (see "Septic Components: Septic Tanks"). On new construction, when septic tank lids are buried more than 12 inches below finished grade, risers or access tunnels are installed on top of the tank lids and are extended up to a point that is less than 12 inches from the ground surface or to grade.

The riser(s) needs to be completely sealed to the tank to prevent ground water from entering the riser cavity, which may cause a flooding of the tank and the whole system. If the riser lid is located at grade, it shall be locked to prevent entry.

Note: The inlet and outlet sanitary "T"'s need to be located directly below the tank access lid for easy access.

Image Septic tank access lid

Image of Septic tank access lid at grade


Septic Components - Distribution 

Gravity Distribution:

Gravity distribution of sewage in septic systems has been the most common design for a long time. Gravity distribution systems take advantage of a natural phenomenon: water flows downhill. Wastewater flows down from its sources to the septic tank, then to the leach lines or absorption area.Image of Septic tank distribution box

Gravity distribution systems have a series of trenches. The trenches are sometimes long (max. 100') and are filled with rock and topped with a fairly shallow layer of topsoil. (See "Septic Component: Leach Lines"). Each trench is connected to the septic tank (usually through a distribution box) so that wastewater leaving the tank flows into the trench - the most typical arrangement of this flow is called "serial distribution".

Serial Distribution:

Serial distribution is a type of gravity distribution where wastewater from the septic tank flows into the first trench until the trench is full. Then the water flows into the second trench until it, too, is full, then into the third and so on. The first trench will tend to be full all the time. When the water level in that trench drops, it will receive wastewater immediately. But aside from the order in which water reaches them, the trenches function independently, each receiving wastewater at the rate it is treated in that trench. If one is draining more slowly than the others, perhaps because it's located in less permeable soil, it will receive less wastewater. If one tends to drain quickly, perhaps because it receives more sunlight and more water is lost Image of Septic distribution box half fullthrough evaporation, it will receive more wastewater. Since the trenches are not directly connected, there is no hydraulic head from trench to trench - water does not move more quickly into or through the second or third trenches because they are downhill from the first one.

Serial distribution allows for flexibility. If one of the trenches fails, another trench can be dug and connected to the septic tank without any alterations to the existing trenches or their distribution lines. Serial distribution also allows for quick inspections - check only the ends of the trenches (See "Septic Components: Inspection Ports").

When the effluent leaves the septic tank, it is sent to the distribution box (D-box). The D-box usually has a single inlet (from the tank) Image of Septic distribution box fulland outlets leading to an individual leach line in the absorption area and another leading to the next D-box.

Other Methods of Distribution - Pipe Fitting

(Crossover Unit) 

 Click here to view Septic tank Distribution box  

  Click here to view Septic diverter cap



Septic Components - Leach Line Trenches

Trenches are long, narrow systems that allow the soil to treat the effluent. The method of distribution is usually gravity (See "Septic Components: Distribution").

The materials used in trenches have changed over the years. Typically, systems have been constructed out of 4" pipe and rock. A number of plastic products have become available recently to replace the rock and gravel-less trenches are becoming more common. (See "Septic Components: Leach Lines").

It is important that the bottom of the leach line trench is a minimum of 5 feet from groundwater to prevent contamination.

It is also important that the bottom of the trench is level, allowing for an even flow of effluent. 


Image of inspectors Inspecting grade
Inspecting open trenches

Image of inspectors shooting grade
To determine the level of the trench bottom, this contractor is shooting the grade



Septic Components - Leach Lines

Leach Lines with Perforated Pipe:

Leach lines are trenches that are filled with washed rock/gravel to flow level. Perforated pipe lays on top of the rock at a level grade. More rock is added to cover the pipe, and paper or other approved filter material is used to keep soil from filtering down into the rock. The paper does deteriorate, but by the time it does the soil is compacted enough to prevent it from dropping into the rock. Perforated leach lines are usually the first choice for a standard individual sewage disposal system design. The pipes of an approved material and are pre-drilled to allow the effluent to trickle through the gravel for treatment. The lines are also shallow enough (12" to grade) for some aerobic bacteria breakdown and some evapo-transpiration.

                cross-section of a leach line.

The area of an individual sewage disposal system's disposal field is sized based on the proposed sewage flow and the soil's percolation rate.

Individual sewage disposal systems are designed to accommodate a sewage flow of 350 gallons per day plus 150 gallons for each additional bedroom.

A standard leach line is considered to be three (3) feet wide and three (3) feet deep with a length as required. A non-standard leach line is wider, narrower, and/or deeper than three (3) feet with a length as required.

Some El Dorado County requirements for standard leach line installation:

  • Maximum length of each line 100 ft.
  • Minimum spacing of lines, center-to-center = 10 ft.
  • Minimum depth of natural earth over all lines as measured from the lowest point of natural grade 12 in.
  • Maximum "drop" in leach line (bottom of trench and drainpipe) 3 in./100'
  • Drain line pipe ends must be capped, holes in pipe must face downward.
  • A minimum of one observation/inspection riser (see: Septic Components: Inspection Riser) shall be installed at the end of each trench.
  • Drain rock/gravel shall be clean, sound gravel or crushed rock ranging in size from 3/4 to 1 1/2inch diameter, with <5% outside this range.

Gravel-less Leach Lines:

InfiltratorGravel-less trench construction (e.g., Infiltrator® systems) may be utilized instead of drain rock in the disposal trench. The design, manufacturing, and materials used shall be durable and acceptable to the Department.

 A single Infiltrator chamber with an end cap.


Some El Dorado County requirements specifically for gravel-less leach line installation:

  • Maximum length of each line 100 ft.
  • Minimum spacing of lines, center-to-center = 10 ft.
  • Minimum depth of natural earth over all lines as measured from the lowest point of natural grade 12 in.
  • "Drop" in leach line (bottom of trench and chambers) shall be as level as possible - max. 3 in/100 ft.
  • A minimum of one observation/inspection riser (see: Septic Components: Inspection Riser) shall be installed at the end of each trench.
  • Scarify (scratch) the trench sidewalls to prevent smearing prior to chamber installation.
  • Provide a splash guard under the pipe inlet to prevent divets in the trench bottom.


Septic Components - Inspection Risers/Ports

Inspection ports, or inspection risers, are vertical pipes that terminate at the bottom of a leach trench and can be opened at the ground surface for inspection. They are found at the end of leach lines and are required to be installed with all new septic systems. inspect_port_pic.jpg

Inspection ports are helpful in monitoring the activity of your septic system. You can monitor the use of each leach line and whether a line is full or not.

It is important to protect your system from surface water, so always keep your inspection port cap on. Also, the pipe extending to the surface should be solid and not perforated. For specific installation instructions, please review the County's Private Sewage Disposal Systems Ordinance, or call your local Environmental Health Specialist at (530) 621-5300.

Inspection port, or inspection riser,
in a trench prior to gravel backfill. Notice the
perforated pipe to solid pipe transition in the trench.
The perforated pipe will be below the filter material


This illustration shows an inspection port / inspection riser installed in a typical gravel-filled leach line:

Image of Septic Inspection port leachine

Inspection ports do not have to be visible in your yard. You can have the port "hidden" in a plumbing box, and it can still be easily accessible for inspection.

Image of Septic port half cover        Image of Septic leachine cover

The illustration below shows an inspection port / inspection riser installed in a typical gravel-less/infiltrator leach line:

Image of Septic inspection port infiltration