P-Trap Vs. S-Trap: What Is The Difference

What Is A P-Trap?

This is a specialized plumbing fitting designed to prevent sewer gases from coming up through the drain line and into your home. The P-trap is made up of two 90-degree joints and a horizontal overflow pipe, creating a U-shaped section where it holds water to create an airtight seal. The function of a P-trap in a plumbing system is to stop noxious sewer gases from entering your home. This plumbing fitting is typically installed under sinks, below bathtubs and showers, floor drains, washbasins, and other plumbing fixtures.

How Does A P-Trap Work?

A P-trap essentially comprises three components—an inlet pipe, a P-shaped bend, and an outlet pipe. The inlet pipe connects vertically downward from the drain of your sink, bathtub, or other fixture. This pipe channels wastewater down into the curved section of the trap.

The P-shaped bend is where the magic happens. The bend retains a small amount of water each time a plumbing fixture drains. The water seal blocks sewer gases from backing up into your home while allowing wastewater to pass. This fitting plays an important role when it comes to odor prevention and maintaining a sanitary environment.

Just like other plumbing fittings, the P-trap can develop a wide range of problems, including clogs, leaks, improper venting, and a dry P-trap. If your P-trap is in disrepair, reach out to a professional plumbing repair service for an inspection. A malfunctioning P-trap can render your home uninhabitable, as it will allow noxious sewer gases to back up into your home.

What Is An S-Trap?

Like a P-trap, an S-trap is a curved pipe designed to trap water and prevent sewer gases from entering your home through the drain. The key difference between a P-trap and an S-trap is the shape. Instead of the distinct U-shape, an S-trap makes a single S-shaped curve.

How Does An S-Trap Work?

An S-trap has a single, gentler S-shaped curve that holds water in an open seal until you flush it. However, this plumbing fitting is rarely preferred in plumbing nowadays due to a number of inefficiencies. The shallow curve holds a smaller pocket of water compared to the deeper U-shaped curve of a P-trap. This smaller water seal is more vulnerable to being siphoned out. If siphoning occurs, it can suck out the water from the S-trap's bend. This defeats the entire purpose of the trap, as there's no water barrier left to stop sewer gases. Due to the higher risk of losing the water seal, most modern plumbing codes prohibit the use of S-traps. P-traps are the preferred choice for reliable and effective drainage with a proper water barrier. If your plumbing is fitted with S-traps, it’s highly advisable to call a plumbing repair service to replace them with P-traps.

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