How to Drain and Vent a Bathroom Sink

Ask This Old House plumbing and heating expert Richard Trethewey helps add ventilation to a bathroom sink that is unvented.

by Richard Trethewey

Skill

Moderate

Cost

$100

Estimated Time

2 hours

How to drain and vent a bathroom sink

An unvented bathroom sink may have a full S-trap, which may siphon and expose the home to sewer gas.
Before doing any plumbing work, turn off the water at the main water supply or at local service valves.
Remove the old drain piping.
If replacing the faucet, remove that as well.
Use plumber’s putty to make a watertight seal on the faucet base plate.
Install the faucet per the manufacturer’s instructions.
Add flexible supply tubing between the faucet and the shut off valves.
Dryfit the PVC drain piping. A P-trap should be used. If venting through the roof is not an option, an air emittance valve can be added at the highest possible place in the cabinet below the sink.
Use plumber’s putty on the drain connections to the sink.
Prime and glue all PVC pieces for the remainder of the drain.

Resources

Richard installed the Vega Single Control Centerset Bathroom Faucet in Brushed Nickel, which is manufactured by Pfister Faucets.

All other parts for this project, including PVC drain piping and an air admittance valve can be purchased from a home center or plumbing supply store.

Tools