AbstractThe fierce positive pressure problem at the bottom of a building drainage pipe system can cause building discharge backflow or indoor environmental pollution. Full-scale discharge experiments on the vent pipe bottom position were conducted in a 60-m-high experimental tower. The vent pipe bottom connected to the drainage stack and to the horizontal main was examined in an H-joint connected dual-stack system and a circuit vent drainage pipe system. Pressure limit values, water seal losses of sanitary fixtures, and airflow rates were investigated to determine system discharge capacities. The maximum discharge flow rate of the H-joint connected dual-stack system with the vent pipe bottom connected to the drainage stack was 7.5 L/s. In comparison, the maximum discharge flow rate of the improved system was increased to 9.5 L/s. For the circuit vent drainage pipe system, the improved bottom connection mode increased the discharge capacity by 200%.Practical ApplicationsA vent pipe end connected to the horizontal main could increase a pipe system’s discharge capacity, which means the system design could adopt a smaller pipe size than usual. This improved connection mode minimizes the material of building drainage pipe systems and reduces associated engineering costs.