The DWV system in your building consists of a series of pipes connected to each fixture; they extend above each fixture, and the system terminates at an open pipe that extends through the roof. This piping allows air into the system and prevents unbalanced pressures in the piping.
The vent also prevents the system from drawing water out of a trap at the fixture with the characteristic “glug-glug-glug” as the drain gasps for air. Plumbing traps should drain smoothly and never “glug” or gasp for air.
If you have a drain that empties slowly or gurgles as it drains, this may indicate a venting problem. If you flush a toilet and the sink gurgles, there’s definitely a vent problem. It is good idea to have a Plumber check this.
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