photo of a septic effluent filter system-photo adapted from US EPA Septic Filters
Guide to Using Septic Filters and Graywater Filters to Protect Drainfields

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Septic filters or graywater filters:

Septic filters are such a significant improvement in septic system operation and longevity that some jurisdictions (such as Arizona) require them on new septic installations.

This document explains the design and use of various types of septic effluent filter systems and graywater filter systems to protect the septic drainfield or absorption system from clogging.

We explain what types of septic or graywater filters are used, where and how they are installed, and how they are cleaned or maintained.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

The Basics of Using Septic Filters to Extend Septic Drainfield Life

Graywater filter basin and filter

While there are several versions of septic and other types of wastewater filters, the most basic septic effluent filter is a simple tee and filter installed at the septic tank outlet. The installation can be handled by a septic contractor or a skilled homeowner, and can cost less than $100. U.S.

Our illustration shows a filter in use in a septic graywater basin.

These simple septic filters, such as greywater filters, washing machine filters, and filters at the effluent outlet of a conventional septic tank are all designed to protect the septic effluent absorption field or leach field.

Septic filters are placed either in the septic tank at the outlet tee or in a separate chamber outside of and close to the septic tank.

Graywater filters may be placed at the inlet to a drywell or graywater disposal system. Washing machine filters are often installed at the clothes washer outlet hose. We include a list of product sources for these various types of septic filters.

[Click to enlarge any image]

Septic Filter Articles

In contrast with septic effluent and graywater filters, media filter septic systems use a conventional septic tank followed by any of several methods to further filter and treat septic effluent before it is discharged to the soil, soil surface, or waterway.

Media filter systems are discussed at Using Septic Media Filters as Components of Alternative Septic Systems for Difficult Sites.

Septic Effluent Filters Protect the Leach Field from Clogging

Photo of a graywater filter system - courtesy of

To add protection for the septic absorption system, add a septic effluent or gray water filter at the septic tank outlet tee. The sketch at page top (US EPA) shows a large basket filter installed at a septic tank outlet.

The photo at left shows a simple filter which is installed inside the outlet tee of a septic tank.

If there is no room in the tank to install such a filter, a small chamber and filter can be installed outside of the septic tank but upstream from the drainfield - just like our septic graywater basin and filter shown in the previous sketch..

Although most grease or large solids entering the septic tank are intended to be retained there where they are reduced to floating scum at the top of the tank or settled sludge at the tank bottom. However septic tank effluent also contains suspended solids, smaller particles of debris which, as they pass out to the soil absorption system, or drainfield, speed the clogging of the absorption system and thus shorten its life.

By trapping more of the suspended solids in septic effluent we pass clarified septic effluent to the absorption system, extending its life. Don't worry about starving the biomat by filtering the septic effluent. There are still plenty of nutrients in the effluent passing into the absorption system.

A number of companies sell these devices which will add life to your drainfield by reducing the level of suspended solids flowing out of the tank. If you buy a septic tank outlet filter you'll see that the filter product will typically be of about the dimensions of the outlet tee I cited above, or perhaps an inch or two deeper.

See the links below for more information about septic filters and septic media filter systems. [Photo courtesy of - see Product Source List below]


Question: Experience Installing a Tuf-Tite EF4 on a Concrete Septic Tank

I just installed a Tuf-Tite EF4 in the outlet of my 30-year-old concrete septic tank, whose outlet elbow had broken off. Very simple job (see comments on the tank tees page), and only took a couple of hours. Total investment maybe $30 - filter was $15, two-foot piece of three inch PVC $4, adapter $5, new can of PVC cement $6. - Brahms 9/29/11


Thank you Brahms for the feed-back. We're thrilled that our article on tank tees was useful and glad to read that your repair went well.

Question: Should I install a septic filter on a tank with multiple baffles?

Is it helpful to install a filter on a septic tank that has multiple baffles? - Deb 12/8/2011


Deb your question is a bit confusing but I am guessing you're talking about a multiple-compartment septic tank, or (more rare) a septic tank with multiple outlets to multiple drainfields. If you have a single tank with ultimately a single outlet pipe that feeds a distribution box and drainfield, you'd install a filter at that outlet end of the tank.

If your septic tank actually has multiple outlets that feed multiple drywells (an unusual installation) you'd need to install a filter at each of them to protect each of the drainfields.

Question: Our septic alarm keeps going off

I just moved to a brand new house and that has a septic. I have septic first time in my life. I have some guest due to family occasion. Alarm goes off every other day. I am told that septic tank pumps 400 gallons a day. If we use more than 400, it sets off alarm. We have 1250 gallon tank and other tank is 1000 gallons that pumps water to drainfield. I have a big family so I will have guest several times a year.

What should I do? Can I pump it manually e.g. total 800 gallons a day until guests are gone? or Should I buy a small pump e.g. 2 hp and pump water out on a small ditch? Can I do that? What is the solution? What is maximum gallons I can have pumped? My drain field is 6 ft deep and about 500 total length.
flag - Jay 5/7/12


Jay this is not a septic filter question, unless your septic tank is backing up because of a clogged septic filter that needs cleaning. It is also possible that your entire septic system, tank and drainfield, was designed with a capacity of processing a maximum of 400 gallons a day.

If you are exceeding the design capacity you will need help from a septic system design engineer to determine the best way to expand capacity of the system. There are other reasons for septic alarms sounding, such as pump or switch problems. Details are at SEPTIC SYSTEM PUMPS and Septic Pump Alarm Systems.

Question: I was told to install a filter at both the inlet and outlet ends of my septic tank.

I was told that i need a filter at both the inlet and outlet of my septic tank . I can't find anyplace that says yes or no . Can you. and why? - T.C.

Reply: Here are the correct options for installing a wastewater filter in a septic system.

The advice you were given, to "install a filter at *both* the septic tank inlet and septic tank outlet) is incorrect and probably comes from confusion about the recommendation for installing a filter at the septic tank (blackwater) outlet and installing filter at a drywell (graywater) inlet. Here are the correct options for installing a wastewater filter in a conventional septic system.

Septic Filter Location 1 - at the septic tank outlet end, baffle, or tee

At the septic tank outlet: a septic tank outlet filter at the septic tank outlet, either as a separate device or as a filter at the outlet baffle or tee protects the drainfields from early clogging by making sure that suspended solids remain in the septic tank.

The septic filter has to be cleaned or changed periodically - the frequency depends on the level of use of the septic system. This septic filter location and application is the principal one recommended by experts. Other than regular septic tank pumpout/cleanout, adding a septic filter at the tank outlet is perhaps the most significant, low-cost improvement you can make that will significantly extend drainfield life.

Details about septic filters are in the article above beginning at FILTERS SEPTIC & GREYWATER

Septic Filter Location 2 - At a washing machine or graywater drain line, ahead of the main sewage line that carries blackwater to the septic tank.

This case applies to buildings whose gray water from a laundry area is ultimately routed to a septic tank that also receives blackwater.

A gray water filter can be installed at a washing machine to extend the life of a septic tank by reducing the load of lint and fibers that otherwise enter the system and that do not readily break down by bacterial action in the tank. This filter would be installed at the washing machine, or at a house graywater drain line ahead of the septic tank and also ahead of any connection to a main sewer or septic line that carries blackwater (sewage, waste from toilets).

Septic Filter Location 3 - Graywater Filters Located at the Inlet to a Separate Drywell

If a building drain system routes gray water, say from a washing machine and perhaps laundry sinks, showers or sinks (but never toilets) to a separate drywell (separate and distinct from the septic tank) intended only to receive graywater, then in that case a graywater filter can indeed be installed at the drywell inlet end to protect the drywell from lint clogging and thus extend its life.

A drywell is intended for graywater only (laundry, sinks, showers), not blackwater (sewage).

Details about drywells are at DRYWELL DESIGN & USES

Do NOT install a filter at the septic tank inlet side nor in the main sewage waste line ahead of the septic tank.

Doing so will prevent solids (sewage, feces, toilet paper) from entering the septic tank and will very quickly, probably in less than a day, completely block the entire drain system leading to backups in the building.


Continue reading at GRAYWATER FILTERS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.




Or see TYPES OF SEPTIC SYSTEMS - master list

Or see these

Septic Filter Articles

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FILTERS SEPTIC & GREYWATER at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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