Some bathroom and kitchen sinks have “S” traps like this one that drain into the floor. It’s important that sewer gas doesn’t get trapped in them.

Proper venting of drain lines ensures that a small amount of water always remains in each household drain trap. In turn, the water in the drain trap keeps sewer gases from escaping into the home.

Bathroom and kitchen sinks with “S” traps that drain into the floor, as opposed to sinks with “J” bends that drain in to the wall, are susceptible to accidental siphoning of drain trap liquid. Adding a spring action automatic air vent or a vacuum activated air admittance valve to a sink drain line can help ensure sewer gases stay where they belong.

Step 1: Choose an automatic air vent for installation on the slip joint piping under the sink or choose an air admittance valve for installation on the heavier glued portion of a drain line.

Step 2: As an added precaution, use the sink shut-off valves to turn off the water supply.

Step 3: With a bucket on hand and a layer of towels under the trap, unscrew the lower portion of the “S” trap from the drain line going into the floor.

Step 4: Use a hack saw to cut the drain line going into the floor about 4 inches below the top of the pipe.

Step 5: Install a 1-1/2″ tee fitting on bottom portion of the cut drain line.

Step 6: Install the top portion of the cut drain line into the tee fitting.

Step 7: Reattach the lower portion of the “S” trap to the drain line.

Step 8: Install a short piece of 1-1/2″ pipe in the open end of the tee.

Step 9: Install a 90 degree elbow on the end of the short piece of pipe.

Step 10: Install a piece of 1-1/2″ pipe into the top of the elbow. The pipe should reach at least 4 inches above the highest point of the “S” trap.

Step 11: Install a female-threaded coupling onto the top of the pipe. Hand tighten the air vent or admittance valve into the coupling.

Step 12: Disassemble, prime and glue together any nonslip joint fittings.

Step 13: Once the drain line is completely assembled, turn the water back on.

Step 14: Fill the sink and let it drain to test for leaks.

Automatic air vents typically last about three years. Make note of the date and plan on replacing the vent before it stops working.

— Have a home improvement question for the Fix-It Chick? Email it to Linda Cottin at features@ljworld.com.