If your vent stack has foul odors the Sweet Air Filter will solve your problem, guaranteed. Stop foul odors from invading your backyards and open windows. This is your answer to eliminate septic odors. The activated carbon will filter foul air which flows through house vents each time a sink, shower, dishwasher, or bathtub is drained, or when a toilet is flushed. Don't be fooled by imitators - these are inexpensive and can be easily installed on existing vents. Designed for use on 3" or 4" sch 40 vent pipe, can easily be adapted for use with smaller diameter vent pipes with inexpensive reducing fittings from your local hardware store. The activated carbon will last several years, actual life of the pellets will vary based on the applications. Features: •Easy to install •Twist top for easy maintenance •Cost effective •Solvent weld connection •Fits existing 3' or 4' sch40 piping •No more offensive odors •No more spoiled patio parties •No more foul air drifting into open windows **When measuring your pipe size be sure to measure the inside diameter of the pipe.