Plumbing vent pipe is very important and supplies air from the atmosphere into the drain pipes. The vent pipes must have slope to drain condensation water. Vent pipes allow air into the plumbing system WATCH my Vent Piping video below! Each fixture needs to be vented properly Vent pipes don’t have.Sluggish drains aren’t always caused by obstructions in the drain lines. Although it might seem counterintuitive, you often can fix them by climbing to the roof, because that’s where the vent openings are located. When the vents get blocked, air can’t get into the drains, and the vacuum produced by rushing .