How to Install a Plumbing Waste Vent System

How to Install a Plumbing Waste Vent System. Your home’s plumbing system contains a myriad of pipes that supply water and allow waste to drain downward and out of the house, but it also includes a vent system, connected to the drainage system, that prevents air locks in the drains. Proper venting prevents clogs and backed-up sewer gas. The main vent system, called the “vent stack,” features a large pipe that runs from the sewer drain all the way up to the top of the house, where it exits through the roof. Individual vent pipes will connect bathrooms and kitchen fixtures to the vent stack.

Drain pipes run downward and vent pipes run upward.

Things Needed

  • Paper
  • Pencil
  • 4-inch PVC pipe
  • 2-inch PVC pipe
  • 4-inch and 2-inch PVC fittings
  • Wrenches or pliers
  • PVC cleaner and glue
  • Chop saw or pipe cutter

Step 1

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.

Step 2

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.

Step 3

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.

Step 4

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.

Step 5

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.

Step 6

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.

Step 7

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.

Step 8

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


  • Because house configurations differ, plumbing drain and vent systems often differ. In the case of a kitchen or bathroom that sits on the other side of the house from the main vent stack, you might have to run a secondary 2-inch vertical vent to the attic and then run the smaller vent to the larger vent.


  • In some communities, a licensed plumber must install all plumbing lines, so contact your local building authority before doing your own plumbing.
  • Local building codes vary. In some communities, you might have to install a specific type of fitting when you connect an individual vent pipe to the main stack. Other codes may specify a different minimum distance between fixtures, and require additional vents.


  • Dave Vandervort’s Home Tips: Drain Waste & Vent Plumbing Systems