The 9-inch ML2-920 effluent filter cartridge from Bear Onsite is designed for maximum septic system ventilation. The open back half enables septic gases to exit through the outlet pipe. It also allows air to come in, replacing the hydrogen sulfide gas and carbon monoxide with oxygen and nitrogen.

“It’s a way to make sure we vent the tank,” says Theo Terry, CEO of Bear Onsite and the product’s inventor.

The filter features horizontal and vertical screens with progressively smaller apertures, allowing polarization to take place for maximum filtration. The size of the primary screen aperture also increases toward the top to open the flow path. Inward folding pleats in the self-cleaning primary screen allow solids to drop into the tank and prevent plugging during periods of little to no flow.

“The initial screen is vertical slots and the final screen is horizontal slots,” Terry says. “The reason that’s important is when solids are rising up in the water column in the housing they’re going to orient themselves with the largest surface area perpendicular to the direction of flow.

“Think of it as a magic carpet,” he says. “It’s going to be laid out horizontally. It wouldn’t be up on the edge. The same is true of solids. If its depth is very narrow, it can go right through 1/16-inch filter because it’s oriented in the same direction as the slots. But if you make that first screen vertical, even if it’s very narrow in depth, you’re going to stop it. We’re not trying to capture solids in filters; we’re trying to keep them in the tank.”

When used with the preinstalled Uni-Coupler, also from Bear Onsite, the ML2-920 filter can easily be used to upgrade the system from a 4-inch Uni-Tee baffle and ML2-916 filter, or the Uni-Tee with multiple brands of filters. The twist-and-lock Uni-Coupler also accepts a 6-inch Uni-Tee or larger housing.

Molded connections enable the ML2-920 filter cartridge to accept an alarm system, while molded-in handle couplings assist in filter changing.

The ML2-920 effluent filter provides 165 linear feet of total filtration and 125 linear feet of 1/20-inch final filtration rated for 1,875 to 2,500 gpd of flow, depending on application.

“When it comes to filters, size does matter,” Terry says. “When you go with a larger filter you have more room for venting, more slots that provide the filtration.”

Accessories include a 9-inch case adapter and three 2-inch Schedule 40 molded-in couplers for adding 2-inch PVC pipe support legs, as well as a 6-inch Schedule 40 molded-in coupler for adding a 6-inch PVC pipe extension and 9-inch plates that slide into the filter case to shut off flow during cartridge maintenance. 877/653-4583; www.bearonsite.com.