A drain trap in plumbing is a device that is used to prevent sewer gases from entering a building. It’s typically a U-shaped pipe that is installed below a plumbing fixture such as a sink or shower. The trap is designed to retain a small amount of water, which forms a seal that prevents gases from the sewer system from flowing back up into the building.
Why are Drain Traps Essential?
The trap is an essential component of a plumbing system because sewer gases can be harmful to human health. Sewer gas contains harmful gases such as methane, hydrogen sulfide, and carbon dioxide, which can cause health problems if they are inhaled in high concentrations. In addition, sewer gas can be explosive, which can be dangerous in certain situations.
How do Drain Traps Work?
The drain trap works by creating a water seal that prevents gases from escaping. The water level in the trap must be maintained to ensure that the seal remains intact. If the water level drops too low, the seal can break, allowing sewer gas to enter the building. The trap must be installed correctly to ensure that it’s functioning properly. The trap must be properly vented to allow air to enter the system and prevent a vacuum from forming, which can break the water seal.
A drain is a pipe that is used to carry wastewater and sewage away from a building and into the public sewer system or septic tank. The drain is connected to the trap, and the trap is connected to the fixture. The drain is typically made of PVC or cast iron and is designed to handle the volume of wastewater and sewage generated by the fixture.
The drain must be properly installed and maintained to ensure that it’s functioning properly. The drain must be properly sloped to allow wastewater to flow freely, and it must be free of obstructions that can cause backups and other problems.
The trap and drain work together to create a functional plumbing system that is safe and effective. The drain trap prevents sewer gases from entering the building, while the drain carries wastewater and sewage away from the building. Both components must be installed and maintained properly to ensure that they are functioning as intended.
Types of Drain Traps, Pros & Cons
There are several different types of traps that can be used in plumbing, including P-traps, S-traps, and drum traps. Something to keep in mind is that not all traps are the same. In fact, the Code of Federal Regulations prohibits certain trap designs. Here are the differences between these three types of traps.
S Trap:

An S trap gets its name from its shape, which resembles the letter “S” when viewed from the side. It’s used in situations where the drain is installed below the floor level. An S trap has a vertical inlet and outlet that are connected by a curved section. The water in the trap creates a barrier that prevents sewer gases from entering the building.
One of the main drawbacks of an S trap is that it’s more prone to siphoning than other types of traps. Siphoning occurs when water flows out of the trap faster than it can be replaced, which can break the water seal and allow sewer gases to enter the building. Therefore, S traps are not commonly used in plumbing, and they may not be allowed by local building codes.
P Trap:

A P trap is named after its shape, which resembles the letter “P” when viewed from the side. It’s the most commonly used trap in residential plumbing. A P trap has a horizontal inlet that connects to the drain pipe and a vertical outlet that connects to the plumbing fixture. The curved section of the trap holds water, which creates a barrier against sewer gases.
One of the advantages of a P trap is that it’s less prone to siphoning than an S trap. This is because the horizontal inlet pipe of a P trap is less likely to create a siphoning effect.
Drum Trap:

A drum trap is a type of trap that was commonly used in older plumbing systems. It consists of a cylindrical container that is installed between the drain and the plumbing fixture. The trap contains a water seal that prevents sewer gases from entering the building.
One of the disadvantages of a drum trap is that it can be difficult to clean and maintain. Debris and sediment can accumulate in the trap over time, which can cause clogs and other plumbing problems.
Another disadvantage of a drum trap is that it’s more prone to siphoning than a P trap. This is because the inlet and outlet pipes of a drum trap are located at the same level, which can create a siphoning effect.
In summary, S traps, P traps, and drum traps are all used to prevent sewer gases from entering a building through the plumbing fixtures. S traps are not commonly used because of their susceptibility to siphoning, and drum traps are less common due to their maintenance issues. P traps are the most commonly used trap in residential plumbing because they are easy to install and maintain, and they are less prone to siphoning.
Drain Traps Prevent Debris From Clogging Sewer Lines
In addition to preventing sewer gases from entering the building, the trap can also prevent other types of debris from entering the drain system. For example, hair and other types of debris can become trapped in the trap, preventing them from entering the drain and causing clogs.
Regular maintenance and inspection of the trap and drain are necessary to ensure that they are functioning properly and to prevent problems from developing. The trap and drain should be inspected regularly for signs of wear and damage. Any leaks or cracks in the trap or drain should be repaired immediately to prevent problems from developing.
About Traps In Relation to Drains
The trap is an essential component of a plumbing system that is designed to prevent sewer gases from entering a building. The trap creates a water seal that prevents gases from escaping, and it must be installed and maintained properly to ensure that it’s functioning as intended. The drain carries wastewater and sewage away from the building, and it must be installed and maintained properly to ensure that it’s functioning as intended. Both components are necessary for a functional plumbing system that is safe and effective.
Need Help With Your Trap? We Got This!
As top rated local plumbers, ensuring the proper working condition of sewer systems, including drain traps is what we do. Whether it’s a P Trap, an S Trap, or a Drum Trap in a slow draining bathroom sink that needs drain cleaning, or perhaps drain repair is necessary because mechanical failure is giving you trouble, we’ll make sure your system performs properly. We’re available 24 hours for emergencies, even on weekends and holidays. Don’t hesitate, call us anytime at 626.448.6455