The STUDOR® MAXI-FILTRA™ operates as a two way vent, which filters air in both directions. Its replaceable active carbon filter is designed to eliminate bad odors produced by the plumbing drainage sysem. The MAXI-FILTRA is for outdoor use only, particularly for use with septic systems, but can also be installed on existing open vent pipes and in systems in which air admittance valves (AAVs) are installed.