How to Install a Plumbing Waste Vent System

Make a diagram on paper of both the home’s drainage system and the vent system. You’ll need a main 4-inch vent pipe that attaches to the sewer main and runs up between wall studs to the roof. A central location in the house for the vent stack is generally better because it’s accessible from most areas. Because a vent system can be very complicated, consult a plumber if you're not sure where to connect a vent.

Attach a T-fitting between the sewer main, which is often in the basement, to the main vent stack. This T-fitting is a 4-inch waste fitting that features a gradual upward sweep to which you’ll connect the main 4-inch vent pipe. When you attach any type of PVC fittings, always use PVC cleaner and PVC glue, according to the manufacturer’s directions, to hold the fittings and the pipes securely.

Run the main 4-inch pipe all the way to the attic. If you use a single pipe, you can cut it later when you attach other vent fittings, but the best way is to add the fittings that will attach to the smaller vent pipes as you install the vertical stack.

Attach 2-inch individual vent pipes to the main vent pipe by installing reducing Y-fittings. A Y-fitting has 4-inch openings on the bottom and the top, to which the main pipe connects, and a smaller 2-inch opening that branches outward from the main vent. Install a Y-fitting so the sweep extends downward, not upward.

Install individual bathroom vents in the wall behind the sink. Since wastewater drains all connect to each other, you usually only need one vent per bathroom, as long as the tub, shower and sink drains all connect within 10 feet of one another. The drain for the sink is the highest drain in the bathroom, since the sink drain has a P-trap and then runs through the wall behind the sink. This makes the sink drain the best place to connect the vent.

Install a 2-inch, sanitary T-fitting in the wall behind the sink. A sanitary T-fitting allows water to drain downward while providing an upward opening for the vent pipe.

Extend the 2-inch vent pipe upward until it reaches the ceiling joists. Install a PVC elbow fitting to attach the 2-inch vertical pipe to a horizontal 2-inch pipe that will then run to the main vent stack and connect with a Y-fitting.

Install kitchen sink vents and clothes washer vents in the same manner.