The vent stack is a vertical pipe that runs from your home’s drain system up through the roof. Its primary purpose is to carry water, but to admit air into the drainage system. This air equalizes pressure, allowing wastewater to flow freely downward by gravity. Without proper venting, the system behaves like a straw with your thumb over the top: liquid gets trapped.
Do not attempt roof work if you have a steep pitch, fear heights, or lack proper safety gear (harness, anchor point). Call a licensed plumber if: clogged vent stack