Polylok’s Activated Carbon vent covers are designed to eliminate offensive odors caused by effluent in your septic system. 2lbs of activated carbon pellets filters and removes often embarrassing odours from escaping your septic system. The specialised activated carbon filter media is integrated into the cover. It is easily replaceable as it is held in a unique filter media bag. Lockable with 6 screws. Green to blend into landscaped areas. The 450mm (18″) cover will fit 450mm (18″) corrugated pipe. Also available in 500mm (20″) and 600mm (24″) sizes.