Eliminates expensive secondary vent stacks. Can be used for sinks, basins, tubs, showers, vanities, and washing machines - not to be used for toilets. 1-1/2" Male pipe threads. Packed 1 per box with installation instructions. Each drainage system using a Mechanical vent must have a main vent stack to atmosphere (through the roof) located so as to vent the water closet. Do not install the mechanical vent in sealed wall cavity - install in a readily accessible location. Installation limited to structures not exceeding 2 stories in height and without corrosive water.