The PL-122 is ideal for septic tanks or the primary tank/chamber of a residential or small commercial wastewater treatment plant. It is rated for up to 5,700 litres per day. It has 1.6 mm filtration slots. Like the Polylok PL-525 & PL-625, the Polylok PL-122 has an automatic shut-off ball. When the cartridge is removed for cleaning, the ball will float up and temporarily shut off the system so solids won’t leave the tank and block percolation area pipes.