The main difference is that a P-trap exits horizontally into the wall and is code-compliant, whereas an S-trap drops vertically into the floor and is generally illegal in modern plumbing. Both trap a small amount of water to block sewer gases, but their plumbing configurations perform very differently.
S traps may not seem dangerous, but they are! They are now banned by many plumbing codes, including Massachusetts, Minnesota, and others. The reason for this is that the “S” shape of the trap, combined with the fact that it does not have a vent, means that water can be siphoned out of the trap.
S-traps are illegal under modern plumbing codes because their unique shape acts like a siphon. When a large volume of water drains, it can suck all the water out of the trap. This removes the protective water seal, allowing hazardous and foul-smelling sewer gases—like methane and hydrogen sulfide—to seep directly into your home.
S-traps are no longer recommended in many modern plumbing systems because they can lose the water sitting inside the bend of the pipe. This problem is called siphonage.
Vertical drain pipe orientation: An S-trap drains water directly down into the floor, unlike the P-trap, which connects horizontally to drainage piping in the wall. Water siphoning issues: S-traps are infamous for causing siphoning.
A straightforward yet effective approach to addressing a clogged drain pipe involves simply using hot water mixed with dish soap. This method, ideal for tackling minor blockages, leverages the degreasing power of dish soap combined with the force of hot water to dislodge and dissolve clog-causing residue.
S traps are generally discouraged or prohibited because they can siphon water out, breaking the seal. Bell and drum traps are less common and may not meet current plumbing codes.
PMRs for malignancies of the stomach, kidney, brain, and lymphopoietic system were also elevated, especially among plumbers. Chronic rheumatic heart disease, emphysema, liver cirrhosis, and all external causes of death were the major non-cancer causes with significantly elevated PMRs.
The best alternative to an S-trap is a P-trap paired with an Air Admittance Valve (AAV). S-traps are prohibited in modern plumbing because water draining through them creates a vacuum that siphons out the water seal, allowing toxic sewer gases into your home.
Over time, repeated use of chemical cleaners can weaken pipe walls, warp plastic piping, and corrode older metal lines. This gradual damage often leads to leaks, cracked pipes, and sudden plumbing failures that require emergency repairs. Another problem is that drain cleaners do not solve the real cause of most clogs.
In plumbing, the "135-degree rule" is a code standard that dictates how much a horizontal drain pipe can bend or change direction. It limits the total cumulative angle of pipe fittings before a system requires an access point (cleanout) or must be vented, ensuring proper flow and preventing chronic clogs.
One essential component of any plumbing system is the trap, a U-shaped pipe designed to hold water and block sewer gases from entering your home. Among the various types of plumbing traps, the P-Trap is code-approved, while the S-Trap is strictly prohibited by U.S. plumbing codes.
Floor drains are an important part of keeping your commercial bathrooms safe and clean in the event of flooding or overflow from toilets, sinks, or urinals.
Pouring salt down your drain at night is a popular DIY plumbing trick used for routine maintenance. The goal is to take advantage of the salt's coarse texture and natural moisture-absorbing properties.
Two common types of traps used in toilet installations are the S-trap and the P-trap. While both serve the essential purpose of blocking sewer gases, they differ in design, application, and compliance with modern plumbing codes.
To protect your plumbing and the environment, you should never put fats, starches, harsh chemicals, or solid waste down your drains.
Let equal parts baking soda and white vinegar gurgle in your drain for about 15 minutes, then flush it down with hot (not boiling) water. Repeat as needed.
J-Traps, also known as J-bends, are designed to create a water seal that prevents sewer gases from entering the living spaces through your plumbing fixtures.
Bottle Trap
Compared to other sink trap types, they're compact and take up much less space making them ideal for ensuite bathrooms and cloakrooms.
10 Things That Your Plumber Wishes You Knew