How to Install Vent Pipe in a Bathroom Drain Line

Vent the bathroom behind the vanity.

The home’s drain, vent and waste system (DWV) depends on gravity and airflow to carry waste and water to the main drain. Drainpipes all slope downward and vents introduce air into the drainage system to prevent water locks. If you’ve ever siphoned water out of a tub with a hose, you know that you can put your thumb over one end of a water-filled hose and lift it out of the tub. The water will remain in the hose until you remove your thumb. All the hose needs is a little air, and the water drains right out.

Things You'll Need

• 2-inch PVC pipe
• 2-inch PVC sanitary T-fitting
• Additional 2-inch PVC fittings
• 4-inch-by-2-inch PVC pipe reducer T-fitting
• Pipe saw
• Measuring tape
• PVC cleaner and glue
• Drill
• 2 1/4-inch hole bit

Instructions

1. Locate the connection in the wall behind the vanity where the horizontal sink drain meets the vertical drainpipe.

2. Connect a 2-inch sanitary T-fitting between these two pipes. The T-fitting has three openings. One fits on the horizontal sink drain, one fits on the vertical drainpipe and the other opens upward for the vent pipe. Where the horizontal opening meets the fitting, you’ll find a sloped angle, called a sweep.

3. Turn the sanitary T-fitting so the sweep runs downward.

4. Cut PVC pipes to fit with a pipe saw and use both PVC cleaner and PVC glue as recommended by the product manufacturers to attach the pipes.

5. Measure, cut and fit a 2-inch PVC pipe to the top of the sanitary T-fitting. The length of the pipe will vary, due to your home configuration, but the goal of the vent pipe is to run upward into the attic, where you will connect it to the main vent and-soil stack.

6. Drill a hole through the top wall plate with a 2 1/4-inch hole bit and run the pipe through the hole and into the attic. Add PVC elbows, where necessary, to redirect the pipe toward the vent-and-soil stack.

7. Intersect the vent-and-soil stack, which is usually 4 inches in diameter, with a 4-inch-by-2-inch PVC pipe reducer T-fitting.

Tips & Warnings

• One vent on a bathroom is generally sufficient because all the drain lines for the bathroom connect to the toilet drain. Behind the sink is the best place because this is the highest drain connection. Both the toilet and the tub/shower connect to the drain in the floor.

• Contact your community’s local building authority before doing any plumbing, even in your own home. You may need a permit, and in some communities, homeowners cannot do their own plumbing unless they are licensed.

References

• Bob Villa: The Plumbing Rough-In