What is an S Trap?

Performing plumbing-related tasks and maintenance can be intimidating for the average homeowner – they do not typically teach you about pipes in school! Fortunately, if you are interested, plumbing can be a lot less intimidating when you learn more about what the different pipes and fixtures are for and how they are supposed to work.

s trap

To help you with your plumbing-related learning journey, today, we will be looking at a type of drain trap called an S trap. What is an S trap?

Keep reading for everything you need to know about S traps!

What Does S Trap Mean?

Located in the drainage pipe beneath the bathroom sink or toilet bowl, the S trap is a pipe that traps a small amount of water after each use to help prevent sewage gases from entering your home. Due to its shape, it also tends to catch any debris or objects that have been accidentally dropped down the sink or toilet. The S trap specifically connects the drain line through the floor.

Do you still need to know more about to answer the question of what is an S trap? Keep scrolling!

How Does an S Trap Drain Work?

When the toilet is flushed, or the faucet is turned on in the bathroom, the water flows down the drain pipe. The S trap in the drain line acts like a vacuum and is supposed to trap a small amount of this water to create a water seal. This water seal is necessary to prevent sewer gases from entering your bathroom.

Why is an S Trap Illegal?

According to the Uniform Plumbing Code throughout the United States, an S trap is illegal because it can actually release sewer gasses into your house. This is because the vacuum that the S trap creates allows the water in the pipe to drain so quickly that it can suck the water right out of it, leaving you with a completely dry trap. This defeats its purpose as a water seal. Therefore, P traps have become the new normal as they will always maintain a water seal due to their shape.

What’s the Difference Between S Trap and P Trap?

the difference between s trap and p trap

While an S Trap has the drain pipe connected to the floor, a P trap instead puts the pipe through the wall. They are named “S” traps and “P” traps due to their shapes resembling those letters. Due to the connection method, the S trap has an extra curve in it that goes up and back down, which points the drain line down instead of straight out like in a P trap.

How Do You Vent an S Trap?

You can try venting an S trap yourself by adding a vacuum-activated air admittance valve or a spring action automatic air vent to your drain line, as well as a waste arm extension (basically just an extra few inches of pipe).

Step 1: Gather Materials

  • Automatic air vent OR Air admittance valve
  • Hack saw
  • 1-1/2″ tee fitting
  • 1-1/2″ Pipe
  • 90-degree elbow pipe
  • Female-threaded coupling
  • Glue
  • Bucket
  • Towels

Step 2: Choose Your Vent or Valve and Turn Off Water Supply

If you choose an automatic air vent, you will be installing it on the slip joint piping under the toilet. If you choose an air admittance valve, you will be placing it on the heavily glued part of the drain pipe. Though you do not have to, you can shut off the water to your plumbing fixture.

Step 3: Unscrew the Drain Line

Look to the drain line going into the floor and unscrew the lower part of the S trap from there. You may want your bucket and towels here to catch any water that may have been trapped in the pipe.

Step 4: Cut the Drain Line

Below the top of the pipe, about 4 inches, cut the drain line connected with the floor with the hack saw.

Step 5: Install Tee Fitting and Reattach

This should first be attached to the bottom part of the cut drain pipe. Then you can install the top part of the line to the tee fitting. The lower part of the S trap can now be reattached to the drain line.

Step 6: Install Pipe and Elbow

Attach a short piece of pipe to the tee’s open end. Then, the elbow can be attached to the other end of the short pipe.

Step 7: Install Coupling and Tighten Vent or Valve

The coupling should be attached to the top of the pipe. The vent or valve you chose can now be tightened into the coupling.

Step 8: Glue Nonslip Joint Fittings

Ensure you take apart, prime, and glue all the nonslip joint fittings.

Step 9: Turn the Water Back On and Check for Leaks

When the drain line has been fully put back together (make sure you have not forgotten anything!), turn the water back on and check for any leaks in the drain line.

How Do You Clean an S Trap?

There are a few different things you can try to clean your S trap. You can pour hot water down the drain pipe, try and use a plunger to dislodge any built-up debris, or use a toilet auger for the toilet or snake for the sink. If you really want to do a thorough clean, you should be prepared to remove the trap entirely.

Step 1: Gather Materials

  • Bucket
  • Wrench or channel lock pliers
  • Brush and/or hose

Step 2: Remove Trap

Look for the S-shaped pipe that is directly under the plumbing fixture. Place your bucket underneath this area so that it can catch any water or debris that comes out when you remove the pipe. Next, unscrew the joints on each side of the trap with the wrench or pliers. Remove the trap from the other pipes.

Step 3: Scrub

Use your brush and/or hose to wash and scrub the inside of the trap.

Step 4: Reassemble and Check for Leaks

Put the trap back together exactly how you found it. Check for leaks by running some water down the drain line.

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