Photo of a graywater filter basin system - courtesy of Guidelines for Graywater Filters to Protect Drainfields & Drywells

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Septic filters: this document discusses the design and use of graywater filter systems to protect drywells or the septic drainfield or absorption system from clogging.

Green links show where you are. © Copyright 2015, All Rights Reserved.

Graywater Filters Protect the Drain Field or Drywell from Clogging

Photo of a graywater filter system - courtesy of

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 drywell or gray water filters.

Also see FILTERS SEPTIC & GREYWATER and see WHAT CAN GO INTO TOILETS & DRAINS?. If your sewer or septic system uses a sewage pump, be sure to review SEPTIC SYSTEM PUMPS and SEWAGE PUMP CLOG DAMAGE.

Just as a septic effluent filter will slow septic drainfield clogging by intercepting suspended solids before they leave the septic tank (or just after the tank if you use a separate septic effluent filtering chamber), gray water from building sinks, showers, and particularly from the laundry, contain suspended solids including un dissolved dry laundry detergent and mostly fabric fibers.

As fabric fibers and solid detergent can clog a graywater disposal system or drywell you can extend the life of these systems by installing a filter at the graywater outlet or at the entry to the drywell. Two common graywater filter points are used and are shown here.

First, a simple "sock" type lint filter (photo at left) can be installed at the clothes washing machine.

This graywater filter method is easy and effective to install for laundry systems that empty from the washing machine into a laundry sink.

We used to use an old pair of panty hose - which works but less effectively than a real lint filter. (Photo courtesy of - see Product Source List below)

Photo of a graywater filter basin system - courtesy of A second graywater filter system uses a filter installed inside a graywater pumping chamber or located between the building drain and the inlet to the drywell or to whatever other graywater dispersal and absorption system is in use.

This system is used for either effluent filtering or gray water filtering when there is not room to install a filter directly in the graywater pumping chamber or in the septic tank. (Photo courtesy of - see Product Source List below).

Filter Chamber Installation: Whether the effluent or graywater filter is installed at the outlet end of a septic tank, the inlet to a drywell, or separately as an interim filtering chamber (as shown here), a riser may need to be installed to permit ready access to inspect and change or clean the filter.

Some states (such as Montana) require that access risers to be least 21" in diameter, and to have an access cover within 6" of grade and even if your state does not, that standard makes sense.

To protect the absorption system, the chamber which holds the filter must (in some states) have a shut off mechanism (such as a ball float switch) so that effluent will not pass through when the filter cartridge has been removed for cleaning or replacement.

When a septic tank riser is installed (to give access to a septic tank cover or to a filter chamber), it replaces the lid (which was on the septic tank at the outlet end, for example) and a new lid is placed at grade to provide convenient access to the equipment.

(Courtesy National Small Flows Clearinghouse, edited and added comments by DJF.)


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Questions & answers or comments about problems with the operation of aerobic septic systems

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

HTML Comment Box is loading comments...

Technical Reviewers & References

Publisher's Google+ Page by Daniel Friedman

Click to Show or Hide Citations & References