How to Install a P Trap to Stop Sewer Gas

What You'll Need
Pipe Sealant
Baking Soda
Warm Water
Chalk or Crayon

Sewer gas can become a source of annoyance, and health risk, in a home where the drain connector or extension drain pipe is not connected to a trap. A p-trap is used to connect the drain connector or extension pipe to the drain pipe in the wall. Although baking soda can get rid of that foul odor coming from the sewer temporarily, a p-trap provides a complete solution.

Step 1 – Prep the Drain System

P-traps are usually installed under sinks. If the sewer gas is coming from the drain opening in a sink, check the drain connector in the underside of the sink. If it is directly connected to the drain pipe in the wall using an elbow pipe, the elbow needs to be replaced with a p-trap.

Purchase a p-trap from a plumbing supply store. Position the trap side by side with the elbow, ensuring that the fittings are facing the proper directions. Determine if the drain pipe and the pipe extension under the drain connector need to be cut. If they do, be sure to add an extension in the pipes to go into the trap fittings. Mark those areas with a crayon or chalk. If the trap needs to be extended to reach the drain pipe coming out of the wall, purchase a coupler to extend the reach.

Step 2 – Remove the Nasty Smell

Before working with the p-trap installation, get rid of the nasty smell temporarily. Mix a pourable solution of baking soda and water and pour it down the drain.  After 10 minutes, follow it through with vinegar solution (1 part water mixed with 1 part vinegar). Leave it for 10 minutes before rinsing it with warm saline solution.

Step 3 – Cut the Pipes

Remove the elbow underneath the sink and detach the pipe extension from under the sink. Cut the extension straight across with a hacksaw. Cut the drain pipe as well if necessary, in order to allow the trap to fit properly into the vacated space. Remove the burrs left behind by the saw, using sandpaper or a file.

Step 4 – Install the P-trap

Reconnect the extension pipe to the drain connector. Dry fit the trap by connecting the horizontal portion to the drain pipe and connecting the other end to the extension pipe or tailpiece of the drain connector. Fit a coupler in between the drain pipe and the trap if necessary. Remove the trap, and adjust the length of the extension or the pipe on the wall if needed.

Before final installation, apply a liberal amount of pipe sealant compound to the fittings on the trap, and secure them to the drain system. Check to make sure that all connections are secure, before leaving the compound to cure overnight. Let water run down the drain. The water will be trapped into the curved portion of the p-trap, and will block sewer gas.