Septic Tank Effluent Filter: Is It Necessary for Your Tank?

An effluent filter is a removable cartridge installed in a compatible housing at the septic tank’s outlet tee or baffle. As wastewater leaves the tank, the filter captures suspended solids that could otherwise enter the outlet pipe and drainfield. Some existing tanks can be retrofitted through an accessible riser, but the outlet configuration must be inspected first to confirm that the filter housing, pipe size, and baffle are compatible. Older residential tanks often don't have any effluent filtration. Effluent-filter requirements vary by system design and applicable regulations. South Carolina homeowners should not assume that every tank has or requires one; the tank and permit information must be checked before recommending a retrofit.

Liquid effluent flows from the septic tank through slots or another filtering surface in the cartridge before entering the outlet pipe. The openings allow effluent to pass while retaining suspended solids inside the tank, where they can be removed during pumping. As material accumulates on the filter, flow becomes restricted. If the filter is not cleaned, the liquid level in the tank can rise and eventually contribute to slow drains or a sewage backup. The filter helps protect the drainfield from solids, but it does not disinfect wastewater or by itself protect nearby wells and groundwater.

A septic tank filter reduces the amount of suspended solids that can leave the tank and reach the drainfield. This may reduce premature clogging, but it cannot prevent failures caused by age, hydraulic overloading, unsuitable soil, damage, or an improperly designed system. Also, it can catch solids that the outlet baffle does not, helping keep them from clogging the drainfield.

The filter should be inspected during routine septic service and cleaned whenever buildup begins to restrict flow. It must also be cleaned each time the tank is pumped. The required interval varies with household use, wastewater composition, filter size, and manufacturer instructions, so homeowners should not assume that the filter can always wait three to five years between cleanings.

Opening a septic tank exposes homeowners to toxic gases, an unsecured access opening, and untreated wastewater. The safest option is to have a septic professional service the filter. When a filter is removed, household plumbing should not be used. The accumulated material must be rinsed back into the septic tank, and the filter should be inspected for cracks, warping, or damaged slots before it is reinstalled. The access cover must then be secured.

GPD capacity is only one factor in selecting an effluent filter. The cartridge and housing must also be compatible with the tank’s outlet tee, pipe diameter, available clearance, permitted system design, and required maintenance access. A septic professional should inspect the existing outlet before selecting or installing a retrofit filter.

PolyLok's filters have a patented design feature where an automatic shut-off ball closes the outlet when you pull the filter out for cleaning. The ball closes the outlet while the cartridge is removed, reducing the chance that unfiltered effluent and solids will enter the drainfield. Household plumbing must not be used while the filter is out because the closed outlet restricts flow from the tank. The SimTech STF-110 effluent filter uses a different design with a bristle cartridge, which is particularly effective at removing hair and lint from the waste stream. Effluent filters provide a level of protection to a septic system that most wastewater treatment systems did not have prior to their introduction.

A clogged effluent filter restricts flow out of the tank. This can raise the liquid level and eventually cause slow drains or a sewage backup. However, similar symptoms can result from an overfilled tank, a blocked or damaged outlet pipe, or a failing drainfield. The filter, outlet baffle, liquid level, and downstream piping should be inspected together before the cause is diagnosed.

We diagnosed a backup on Laurelton Place in Greenville, where the septic tank’s outlet pipe, not a filter, was blocked. An effluent filter protects against solids in the tank reaching the drainfield, but it can’t fix a broken outlet pipe. Both problems start at the same spot, so inspect the filter and the outlet together.

Call (864) 431-2822 before pump-outs, and we’ll inspect the filter, the baffle, and the outlet at once across Spartanburg, Greenville, Cherokee, Pickens, and Anderson counties.