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NC State Extension

Outlet Filter Devices

Approval Standards for On-Site Sewage Treatment and Disposal Systems
Outlet Filter Devices

Paul Booher, PE
Bureau of Water and OnSite Sewage Programs


  • FILTER AREA–Specify total filter surface area, in square feet, (filter solid area plus filter void area)
  • FLOW AREA–Specify filter open area, in square feet, (filter void area only)
  • FILTRATION METHODS–Filters shall prevent solid particles larger than a nominal 1/8″ diamter sphere from passing through the opening.
  • CLOGGED FILTER BY-PASS PROTECTION–there shall be no bypass capability designed into the filter which will allow waste to be discharged.
  • FILTER DESIGN–Filter orifices shall be formed by casting, molding, or developed by penetration or sawcut. Openings developed by penetration, sawcut or equivalent shall ensure the complete removal of the filter material to prevent the openings from reclosing during the lifteime of the filter. The designed opening shall be process controlled and the material must be removed. Mold flash and penetration burrs shall be completely removed.The filter shall be secured to the outlet device rooutlet opening such that inadvertent movement does not take place during operation. the dimensions of the filtering components shall be consistent throughout. For example, the distance from the filter mesh to the outlet device inside wall shall not very outside of process control limits.
  • STRUCTURAL INTEGRITY–the filter shall be designed such that thefiltering medium maintains structural integrity throughout the useful life of the device. The filter medium shall not tear or otherwise distort so as to make the filter inoperable during normal operations of the septic tank.

OPERATIONAL VERIFICATION–The manufacturer shall provide results of field testing for their product(s) being considered for approval.
DRAWINGS–Manufacturer shall provide drawings to the Department with the written request for product approval submittal. Drawings shall show all dimensions.
FREQUENCY OF MAINTENANCE–Manufacturer shall provide data and information reflecting actual operational experience related to the frequency of necessary unit maintenance to keep the unit functional and shall specify the recommended method and frequency of maintenance.
INSTALLATION INSTRUCTIONS–Manufacturer shall provide installation instructions to installer.
MATERIALS OF CONSTRUCTION–the filter shall be constructed of proven corrosion resistant material for use in wastewater environments.
MAINTENANCE ACCESSIBILITY–64E-6.013(3)(b),FAC requires accessibility to the inlet and outlet devices. When outlet filter devices are used, this rule shall include convenient accessibility to the filter for maintenance through servece manholes or equivalent.
CERTIFICATIONTO DEPARTMENT OF HEALTH, ONSITE SEWAGE PROGRAMS–The manufacturer shall certify to the Department that the filter(s) meet the requirements of this standard.
FILTER APPLICATION–Filters shall be sized in accordance with the manufacturers’ recommendations for the service intended.