Sealed Off Building Drainage and Vent System

A drainage and ventilation system for a building is provided which includes two or more stacks which communicate fluid therein. The stacks are connected to a sewer for discharging liquid thereto, with at least one of the stacks having a discharge source for delivering liquid to a wet stack portion of that stack. A trap is positioned between the wet stack portion and the discharge source for inhibiting the passage of gas therethrough. The stacks are interconnected at an upper end thereof by a connecting member such as a connecting pipe or manifold, whereby air may be communicated between the stacks. An air admittance valve and a positive air pressure attenuation device are located above the connecting member, whereby air may be introduced into the stacks to compensate for entrained air moving with the liquid into the sewer, and air may be accumulated during increased pressure events, both helping to preserve trap seal integrity without releasing foul air into the surrounding environment.