The Sieve That Will Save Your Customer’s Onsite System

Effluent screens are the necessary last line of defense against a plugged drainfield and costly system repairs.

The Sieve That Will Save Your Customer’s Onsite System

This effluent screen has stopped foreign objects, such as wipes, from being carried to the drainfield.

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Recently I have had a few reports of effluent screens plugging with frequencies of less than a year, requiring more frequent cleaning. So I thought it would be a good time to discuss the purpose and operation of effluent screens while offering a few thoughts on why some residential screens plug more often, requiring increased maintenance.

I have written numerous times that septic effluent quality is a key to the longevity of the soil treatment and dispersal area. Installing an effluent screen at the septic tank outlet helps reduce excessive organic solids or other non-organic solids from being delivered to the drainfield. Most often, these devices are fitted into the outlet baffles of the septic tank, although some varieties are installed outside of the tank with a separate access point for cleaning and maintenance. 

Originally, the focus was on preventing larger organic solids from plugging soil, resulting in drainfield failure. Presence of the screen keeps drainfields relatively clear. Additionally, presence of a screen at the outlet keeps other types of solids from causing problems in drainfields. This includes floatable plastics or cleaning wipes from moving through the system and creating blockages.


Recently, the most common item being kept from damaging the drainfield are all manner of antibacterial wipes. They were a problem before the pandemic, but with the increased use and some erroneous information about their flushability, problems have been occurring in municipal sewers as well as individual septic systems.

Many states and municipalities now require effluent screens in onsite systems. In Minnesota, they have been required since 2011. They can be installed either in new or retrofitted in existing systems. The screens are relatively inexpensive and they work without moving parts. 

They do require regular maintenance to keep the outlet from totally plugging, resulting in sewage backing up into the house. This means there should be easy access to the screens so they can periodically be cleaned. 

Manufacturers generally recommend servicing the screens every 1 to 3 years, which typically corresponds with recommended times for tank maintenance. To guard against backups, the recommendation is to have a high-water level alarm so the homeowner can have the unit serviced before the backup occurs. In some states, including Minnesota, an alarm system is required.

If the effluent screen seems to need cleaning more often than normal, it probably indicates there are system use issues resulting in too many solids, cleaning chemicals or water being added to the system. What are some overloading causes to look out for?

Large volumes of wastewater delivered to the tank in a short period of time can result in turbulence in the tank, preventing solids from settling properly and resuspending some of the settled sludge. Suggest the homeowner try to spread the laundry out during the week instead of doing it all in one day. In addition, recommend they not run multiple water-using devices at the same time. This means not showering or running the dishwasher at the same time as doing the laundry. 


Another potential problem with the laundry is adding lint to the septic tank. To avoid this, a lint filter can be attached to the end of the outlet hose. Of course, this means the homeowner will have to remember to periodically clean the filter.

Dishwashers and garbage disposals can be significant sources of solids to the tank. As I have said many times, homeowners should be encouraged not to have a garbage disposal. Suggest they have a compost pile or place food scraps in the garbage. Many of the newer dishwashers have built in garbage disposals. All dishes should be scraped well before putting them in the dishwasher. This does not mean rinsing the dishes! Rinsing dishes can add significant amounts of water to the system, often more than running the dishwasher itself.

Nothing other than bathroom tissue and human waste should be flushed down the toilet. The homeowner should be encouraged not to flush cleaning wipes, cigarette butts, hygiene products or facial/makeup tissues. All these extraneous products can rapidly move through the tank to the screen and plug it.

Excessive use of strong cleaning agents (products with bleach) and antibacterial soaps can kill or inhibit bacteria in the tank. This will reduce the rate of solids decomposition and cause increased movement of solids to the tank outlet. The same recommendation can be made to flushing unused or expired medications. These medicines can interfere with tank bacteria and they should be taken to a medication drop site. Most pharmacies will dispose of unused medications.

An additional contributor to excessive plugging is the growth of bacteria, slimes and algae in the screen. This can be exacerbated by the construct of the filter itself, changes in pH and chemistry within the tank, and additions of water from water treatment devices (softeners and iron filters, etc). If there is excessive plugging, make sure the screen has vertical openings so excess solids will have a tendency to slough off and drop to the bottom of the tank rather than plug the holes.

As a final note, the effluent screen needs to be durable. If you find the screen installed is flimsy and does not stand up to multiple removals and cleaning, recommend the homeowner have a different screen installed.  


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