Guidelines for Graywater Filters to Protect Drainfields & Drywells InspectAPedia® -
Graywater filters & how to use them to protect the drywell or drainfield
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This document discusses the design and use of graywater filter systems
to protect drywells or the septic drainfield or absorption system from clogging.
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.
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Graywater Filters Protect the Drain Field or Drywell from Clogging
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 thenaturalhome.com - see Product Source List below)
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 thenaturalhome.com - 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.)
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