photo of a septic effluent filter system-photo adapted from US EPA Septic Tank Effluent Filters, Sewage Filters, Maintenance Guide & Procedures for Homeowners
     


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Septic & graywater filter maintenance: this document discusses when & how to clean or maintain septic filters and graywater filters to protect the septic drainfield, drywell, or absorption system from clogging. 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 to catch solids of various forms and thus to significantly extend the life of a drainfield, drywell, or soakaway bed. But how do we know when to clean the septic or graywater filter & how do we know if it is clogging? We also discuss methods for monitoring the condition of the septic or graywater filter.

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Septic or Graywater Filter Maintenance Procedures

Washing machine filters are often installed at the clothes washer outlet hose. Media filter systems (which unlike filters at the septic tank or drywell, are used to treat septic effluent) are discussed at Using Septic Media Filters as Components of Alternative Septic Systems for Difficult Sites.

Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Reviewers & content suggestions are welcomed and are listed at "References."

Septic filter or gray water filter maintenance is essential to keep the septic system working properly. Failure to clean the filter can lead to slow drainage in the building, clogged drains, and backups at the septic tank or drywell. The advice here combines suggestions from septic filter or screening product manufacturers and the experience and field reports from people whose septic system design includes filters and screens.

Septic or graywater filters need regular cleaning

Installing a septic effluent filter or gray water filter on a wastewater disposal system can be a comparatively inexpensive, cost-effective step you can do to extend the life of the drain field or soil absorption system. However, as the filter clogs it can cause a too-sluggish release of effluent into the drainfield and it can even result in a septic system backup. For this reason if you install a septic effluent filter or a gray water filter, regular inspection (monthly) and filter cleaning on schedule are very important.

These steps involving use of effluent filters, pumping the septic tank on schedule, conserving water use, and watching what you flush down the toilet comprise a list of key steps to get the most life out of onsite wastewater treatment and disposal systems.

Is a septic filter actually needed at a septic tank?

According to NSF, "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. We particularly like to see a washing machine filter installed at homes using a septic tank since the lint (and sometimes clots of un-dissolved detergent) can add significantly to septic system clogging.

We often recommend a septic effluent filter to help protect drainfields which themselves have limited capacity or at sites with poorly-absorbing soils. If the septic tank is maintained properly, including frequent inspection for solids accumulation and removal, then a filter may not be necessary" -- www.nsf.org/consumer/wastewater_treatment_systems/wastewater_filters.asp?program=WastewaterTreSys

Does pumping the septic tank mean the septic filter does not need to be cleaned?

Some people argue that if the tank is pumped regularly (SEPTIC TANK PUMPING FREQUENCY), cleaning the septic filter "may not be necessary". This is a questionable notion at best. Think of it this way: if a septic filter or graywater filter never ever needed to be cleaned or replaced, it must not be filtering anything out of the effluent stream in the first place! In any case, local building code or health departments may require an installation permit and/or may require that the septic filter meet NSF/ANSI Standard 46.

In sum:

  1. You don't have to install a septic filter at the septic tank to protect the drainfield from clogging if the septic tank is properly maintained - that is, pumped on an appropriate schedule, and provided that you don't do something foolish such as use septic system additives (such as yeast) which cause agitation or frothing inside the septic tank, interfering with sludge settlement and formation of the scum layer. Interfering with these processes risks pushing high levels of suspended solids into (and clogging) the drainfield.
  2. Having a septic filter installed adds extra protection for the drainfield and extends the probable life of the drainfield
  3. If you have a septic filter or graywater filter installed, it is very important to clean the filter regularly

How often to clean the septic or graywater filter

The actual cleaning frequency needed for sewage filters, filtering basins, infiltrator chambers, wastewater filters, or effluent filters may range from every few months to every few years, depending on system usage, wastewater flow, septic system design, and the type of filtration used.

The septic system or graywater system filter cleaning schedule will normally be based on the estimated wastewater flow for the building. Home & Outdoor Living Water Quantity Requirements and also Table of Required Septic Tank Sizes are two articles available online that may assist you in estimating your daily wastewater flow if you don't already have that figure.

After having the septic tank pumped and cleaned (or the drywell opened and inspected) and having cleaned the filter the first time, follow the septic filter manufacturer's recommendation for cleaning frequency.

If you cannot find the manufacturer's septic or graywater filter cleaning recommendations or if you don't know your wastewater usage level, try checking the filter again in six months. If there is no significant clogging, check it again in another six months. Following this procedure you can determine, based on your own building's wastewater usage and flow, just how often to clean the filter.

We recommend that you establish a regular filter inspection and cleaning schedule. If you've purchased a home that uses one of these filters and have not already done so, schedule a septic tank pumpout and cleaning and inspect and clean the filter at the same time.

Septic filter monitors are available from some effluent filter manufacturers to help determine when it's necessary to clean the filter.

If there are signs of septic filter or graywater filter clogging before you reach the next schedule filter cleaning date, you should increase the cleaning frequency accordingly.

How to clean a septic filter or graywater filter

A great time to clean the septic system filter is immediately after the septic tank has been pumped. The empty septic tank means that when you remove the septic filter for cleaning, no sewage will bypass it and flow into and clog the drainfield.

Most septic filters and graywater filters will need to be inspected and cleaned more often than the septic tank is pumped out. (Most drywells are not pumped or emptied during servicing.) Just above we discussed how to come up with a schedule for filter cleaning.

The access cover is opened, the septic filter itself is removed and washed, typically by spraying it with a hose. Avoid getting overspray on anyone as it is not sanitary. Replace the filter and wash your hands.

How to avoid damaging a drainfield when cleaning the septic filter

Temporarily stop running water in the building served by the septic tank during the septic filter inspection and cleaning process. By avoiding sending wastewater into the tank during this interval, you're avoiding pushing sewage out into the drainfield during the time that the filter has been removed for cleaning.

Check the sewage level in the septic tank: If the septic tank is opened at the access port to inspect and clean the septic filter, before removing the filter cartridge or screen check the level of sewage in the septic tank. If the tank wastewater level (floating scum, effluent, sludge) is abnormally high that indicates a system blockage (maybe a clogged filter).

Do not remove the filter if the tank level is abnormally high since doing so will flush extra sewage, solids, floating scum, grease, into the drainfield, potentially clogging it or shortening its life. If the tank level is abnormally high (flowing over the inlet or outlet baffle or if the tank is filled to the very top) it would be better to have the tank pumped before removing and cleaning the filter. If even after these steps are taken (septic tank pumping and septic filter cleaning) the tank level returns to an abnormal level, there is a further blockage in the septic system, in the distribution piping, distribution box, or drainfield, and further investigation is needed.

How to monitor septic or graywater filters for clogging

Be sure to review Signs of a Clogged Septic Tank Filter. If your septic or graywater filter has become clogged, it needs more frequent cleaning.

Septic Filter Installation: make sure the septic or graywater filter is easily accessible

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.

If the cover at the septic filter or graywater filter is not easily accessible, excavate to expose it and install any necessary surrounding riser and ground-level cover. In other words, make the task as easy as possible so that the septic or gray water filter inspection and cleaning process is painless and will be done on time. These steps will more than pay for themselves in keeping the septic system working and maximizing the life of the drainfield.

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