This diagram represents a residential DWV (Drain-Waste-Vent) system. In plumbing, there are two distinct flows happening simultaneously in these pipes: 1. Gravity (Waste/Water): Flows down to the sewer. 2. Air (Venting): Flows up to the roof to balance pressure and allow the water to move smoothly without gurgling or stopping. 1. The Venting System (The "Lungs") The pipes extending upward are crucial for air circulation. Without them, water would get stuck (like putting your finger over a straw)