Types of Drain Traps

In this blog post, you’ll read:A trap is a plumbing device with a curved pipe channel that holds fluid to block sewage gases from entering a building while allowing solid waste to flow out. Most commonly used shapes for traps in residential plumbing include U, S, Q, and J. Wastewater

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A trap is a plumbing device with a curved pipe channel that holds fluid to block sewage gases from entering a building while allowing solid waste to flow out. The most commonly used shapes for traps in residential plumbing include U, S, Q, and J. Wastewater, known as sewage, is a source of harmful gases. Methane, carbon monoxide, and hydrogen sulfide are a few examples of the toxic gases that can be released. Even if we can’t stop the waste from decomposing and releasing harmful gases, we can keep them out of the house! Gases released from sewage treatment plants might cause minor diseases or even death. That’s why traps in the plumbing system become essential now.

Role and Significance of Drain Traps

A trap is a component of the drainage system. It is developed or designed to retain a small amount of wastewater from the discharge of the fitting to which it is affixed as a barrier to prevent harmful gases or air from entering the structure. Traps are an essential component of the sewerage system. They prevent filthy air, insects, and parasites from entering the building from the sewers and prevent the spread of disease. Traps are designed to retain a body of water that functions as a water seal. Self-cleaning traps should be utilized. They should generate sufficient motion from the available flow to create a self-cleaning effect, i.e., a flat surface and a uniform opening. Maintaining the water barrier is crucial to the operation of traps; traps can dry out, and insufficient airflow can suction water out of the traps. This is typically avoided by venting the drain pipes downstream of the trap; by venting to the atmosphere outside the structure, the drain lines never operate at pressures significantly above or below atmospheric pressure.

Types of Drain Traps

The types of traps in plumbing are as follows,

  1. Gully Trap
  2. P Trap
  3. S Trap
  4. Q Trap
  5. Floor Trap / Nahni Trap
  6. Bottle Trap
  7. Intercepting Trap
  8. Running Trap
  9. Drum Trap
  10. Straight-Through Trap
  11. Low-Level Bath Trap
  12. Building Trap
  13. Bell Trap
  14. Grease Trap

Let’s dive into the explanation of each trap.



S-traps are the type of trap that prevents sewer gases from entering basins and other plumbing equipment. The S-shaped pipe design captures wastewater before it enters the sewer line, making a water seal that stops vapors from rising through the drain. P-traps were prevalent early in the 20th century but are no longer used. When a large volume of water passes through the S-trap, it may produce excessive suction, causing water to be sucked out of the trap and dry. The air opening made by the dry trap allows wastewater gases to enter the structure.

Modern plumbing regulations no longer permit s-traps. Most, if not whole, jurisdictions in the U.S. have banned using S-traps in new construction, and S-traps must be replaced with P-traps in older buildings.



P-traps contain u-shaped bends in P-traps that filter incoming effluent as it enters the drainage system. One end of the trap is connected to a sink, bathtub, and shower via a J-bend, and the other is connected to your drainage system. The J-bend is the p-trap section that resembles the letter J.

The p-trap’s bend captures water in the curve, creating a 1-1/2- to 2-inch water seal at the weir and preventing sewer gas and contaminants from entering the residence. The weir is the upper bend of the p-trap, where the water begins to overflow into the wall duct. When the fixture is used, new effluent is flushed through the p-trap, changing the old water in the curved area with new water.

Material for P trap:

Brass and plastic are two materials that are used to make p-traps. Even though they both play the same role in the water system, each material has its pros and cons.

  • Chrome plating makes brass p-traps look elegant. On the other hand, brass can and will rust over time if it is used over and over again.
  • Its plastic counterpart, polypropylene, is not as appealing, but it doesn’t rust or interact with acids because it is lightweight and comfortable to put together and take separately if necessary.


  • An important advantage of using a P-Trap system is that it effectively prevents sewer gases from entering a structure.  
  • The P-Trap’s water seal prevents these gases from escaping and infiltrating the living space by acting as a barrier.
  • It prevents debris from clogging the infrastructure, reducing the risk of backups and overflows.

Where it used

  • Used in shower, bathtub, kitchen sink drain system, etc.

Gully Trap

Gully Trap
Gully plastic Trap

G.T. trap is the name of the gully trap. The plumbing trap captures kitchen and laundry basin water. Then, it is connected to the main sewer line. Therefore, the gully trap connects the residence’s water lines to the drainage line.

A mesh is installed in the drainage trap to prevent debris. The water seal’s height in the gully trap is between 60 and 70 mm. Less than 1 foot of ground is typically required for effective connection and installation of alley traps.

The seal should be at least 50 millimeters wide for water seal integrity in alley traps. To prevent insects and harmful pollutants from getting into your home. These traps are constructed in various locations within various sewer pipelines. Heavy cast iron gully traps must weigh at least 7.25 kilograms (16 lbs), have a cover weighing at least 4.53 kilograms and a frame weighing at least 2.72 kilograms, and have a minimum depth of 30 centimeters (1 foot).

Advantages of Gully Trap:

  • Easy Maintenance:

Gully traps are typically designed with removable covers or grates, allowing easy access for cleaning and maintenance. This makes removing accumulated debris or sediments convenient, ensuring the trap functions optimally.

  • Flexibility:

Gully traps can be installed in various locations, such as driveways, outdoor areas, or near plumbing fixtures. They can be customized to fit different pipe sizes and configurations, making them adaptable to different plumbing systems.

  • Longevity:

Gully traps are commonly made of durable materials such as cast iron, PVC, or stainless steel, which resist corrosion and wear. This ensures the traps have a long lifespan and can withstand the outdoor elements.

  • Compliance with Regulations:

Many building codes and regulations require the installation of gully traps to maintain proper hygiene and prevent foul odors. Installing gully traps ensures compliance with these standards.

Floor Trap | Nahni Trap

Floor Trap

The floor traps are also referred to as Nahni Traps. Nahi Trap is provided to prevent toxic gases from entering the structure by providing a water seal. At least 50 mm of water seal depth must be provided. If drain water flows, a floor trap prevents toxic gases (awful odors) from entering the building. To collect wastewater from the lavatory, laundry area, washbowl, and kitchen sinks, a floor trap or Nahni trap is installed on the floor. Floor traps are available in PVC, UPVC, and CI; they lack vent pipelines, but removable grinding is displayed at the top of the Traps.

The length of the floor trap is 310 mm, with a width of at least 80 mm at the channel end, 30 mm near the outlet end, and 73 mm outside the floor trap outlet. In addition, the 95 mm grinding size resulted in the enormous floor trap with 8 mm measurement apertures. It captures water from the kitchen, lavatory, and floor. It is made of PVC-coated cast iron.


A Q-trap is suitable for upper levels if your building has multiple floors and restrooms. Except for their distinctive “Q” design, they function similarly to P-traps and S-traps. Q-traps are standard plumbing traps that utilize water and pipework to prevent wastewater odors.

Like the P-trap, the Q-trap captures water in its body’s “U”-shaped region, and both are efficient. The available space under the sink heavily influences the decision between a Q-trap and a P-trap. You will never have to fear your Q-trap drying out if you consistently stream water through it. W

Where it is used:

  • These kinds of plumbing traps are used in the latrine-submerged storage area.

Intercepting Trap

Intercepting Trap

In the Interceptor Chamber, plumbing trap types are intercepted. There is an interceptor sewer discharge at the intersection of the building sewer and the public sewer. Homeowners are not required to install intercepting traps, although they are common in large buildings and blocked sewage systems. They are practical and capable of managing substantial amounts of waste from various plumbing applications in a large building. Most office buildings and large corporations require intercept traps to meet their hygiene needs while preventing the escape of sewage smells.


  • Due to their durability, intercepting traps prevent insects and other rodents.
  • Intercepting traps are more complex than standard plumbing traps due to their extensive roles.
  • In massive buildings, intercepting traps are located in the final primary opening where the sewage system enters the structure.

Where it is used:

  • Used in the street sewer to prevent foul gases

Grease Trap

Grease traps are the last line of protection between a kitchen and the sewer system. They work to stop thick oil and solid pieces from getting into a kitchen’s wastewater system and causing damage.

Grease and solid trash from cooking can’t get through a grease trap because they are thick. It keeps the pipes from getting clogged or leaking grease, which could be dangerous and costly to fix or replace. On the other hand, a grease trap stops the heavy oil at the top of the trap from becoming a problem.

Where it is used:

· Use in the hotel’s drain system

  • In every restaurant and fast food place, grease traps are used.

Bottle Trap Gully

The waste pipe is set up horizontally in this type of trap, and to clean it, you have to unscrew the bottom. Bottle traps are often used at pedestal-mounted sinks and basins to trap smelly gases. They are simple to fix and do not require too much room. This trap is more significant than the pipe that goes into the basin. When water is put into the trap, it fills with fresh water. Because of this, there is some water in the trap.

Where it is used:

  • Below the sink and wash basin to stop the bad smell.


  • Easy to maintain
  • Bottle drain does not require replacement for a long time
  • There is always water in a water seal
  • If a small thing falls into the drain, it is easy to collect it by unscrewing the bottle.

Drum Trap

Drum Trap

The large openings of drum traps, which resemble metal drums, are essential to a home’s plumbing system because they make it easier to locate and remove objects that need to be retrieved or removed from the plumbing system. Their large covers also make it simple to insert a plumbing snake into the trap to unclog your drain. Water from a drainpipe in your residence enters the trap from the trap’s bottom and then exits from the trap’s top, leaving behind solid debris.

Advantages of Drum Trap:

  • Drum traps can accumulate sediment, debris, and solid waste over time, which may act as a trap for materials that could otherwise block the drainage system.
  • Drum traps typically have a larger volume compared to other types of traps, such as P-traps or S-traps. This larger capacity may be beneficial in specific applications where a higher flow rate or larger amounts of wastewater are expected.


It’s vital to note that drum traps also have many drawbacks. This led to their decreased usage and, in some cases, their prohibition of current plumbing codes. These disadvantages include:

  • Clogging and maintenance challenges
  • Limited accessibility
  • Restrictions in current codes

Building Trap

Building traps consist of a U-shaped trap in the middle and an outdoor vent at the end; they travel from a building’s drain to the sewer. Ventilating a building trap is necessary to keep it sanitary and maintain the water closure. In order to accommodate the increased demand, building traps typically take the form of a larger, more stable S-trap. They are equally effective at repelling odors to keep insects and rodents away from a home or structure.


  • Using building traps prevents hazardous siphonage, which could release poisonous gases from the drain.


  • It is against U.S. building regulations to fail to vent a building trap.

Running Trap

These are often found in public bathrooms, where a single running trap is used to catch several washbasins that have not been captured. It could be used in homes without a P or S trap setup. Even though these machines have their traps, running traps are sometimes used with the waste from a washing machine or dishwasher.

Material and Diameter:

Running traps are available as one-piece units. The pipe has a Schedule 40 thickness and is manufactured from PVC [polyvinyl chloride]. It has a diameter of 34 inches and a length of 10 inches. The varieties of connections for the inlet and outlet are solvent weld.


Running traps are ideal for condenser discharge lines on air conditioners. You save fitting, welds, and sealants because they are sold in one piece. Due to its simple structure, it is simple to implement, thereby reducing labor costs.

Low-Level Bath Traps

Low-level bath traps provide overflow access, which is helpful if you have a clog. Low-level bath trap closures are typically 38-40 millimeters in diameter and are simple to vent. Low-level bath traps might seem insignificant, but their seals are robust enough to prevent sewage odors from entering.

Where it uses:

Due to their ability to be set in tight spaces, low-level bath traps are ideal for installation beneath a bathtub or shower. It may not suit all vent stacks, but a low-level bath trap is worth the cost.

Straight Through Trap

Straight Through Trap

This type of trap has an inlet and outlet of 11/4 inches and a cleaning eye. It features a 75 mm water seal. This form of trap is composed of polypropylene. These are used when there is insufficient space for a snare. Additionally, they are more concealing beneath pedestal basins—an alternative valve functions on the premise that an interior membrane creates a seal. When water is discharged, the membrane allows water to pass through before closing to prevent foul air from entering the structure.


  • Cost-effective
  • Space saving
  • Enhance the flow efficiency
  • Reduce blockage risk

Idea for:

  • This trap is best for basins with pedestals.
  • It is also utilized as a substitute for the trap where the space is limited
  • It comes in different adapters, which makes it ideal for various applications  

Drain Trap Size for the Different Types of Fixtures

Fixture Trap Size (in)
Floor drain2
Bidet1 ½
Bathtub1 ½
Kitchen sink1 ½
Dishwasher1 ¼
Lavatory1 ¼
Drain trap sizes

Buying Guide to the Drain Traps

Before buying the traps for your fixtures, keep in mind the following main factors.

Size and Configuration: Consider the pipes’ diameter, the trap seal’s required depth, and any space limitations. Proper sizing and configuration will help maintain proper flow and prevent potential issues such as clogs or reduced drainage efficiency.

Performance and Odor Control: Look for traps with sufficient water seal depth and proper design features that minimize the risk of trap siphoning and odor issues.

Trap Material: Drain traps can be made from materials like PVC, cast iron, brass, or stainless steel. The choice of material should consider factors such as durability, resistance to corrosion, and suitability for the intended application.

Ventilation: Adequate venting helps maintain the water seal, prevent trap siphoning, and allow for the proper flow of wastewater. Consider whether the trap requires a dedicated vent or relies on the venting provided by the plumbing system and fixtures.

Maintenance and Accessibility: Some trap designs have removable covers or access points, making them easier to clean and inspect for blockages or debris. Ensure that the trap’s design allows for convenient maintenance without compromising its functionality.

Local Codes and Regulations: Plumbing codes and regulations may have specific requirements for drain traps. Consult local codes to ensure compliance with ventilation standards, trap seal depth, trap material, and any specific trap types allowed or prohibited in your area.

Siphon and pipes under the sink in the kitchen.
Siphon and pipes under the sink in the kitchen.

What is the specification of drain traps?

For appropriate reinforcement, the trap must be made of quality materials.

  • The trap should be adequately filled with water to prevent the entry of harmful gases into the home.
  • The interior surface of the trap should be seamless, allowing water to escape quickly.
  • The trap should be of high quality so that the water cleans itself.
  • The trap’s surface should be smooth and devoid of grooves so water can drain readily.
  • The design of a trap must be simple and cost-effective.
  • The trap should be simple to install with the drain.
  • The gully trap is equipped with a mesh to prevent debris from entering. The water seal’s height in the gully trap is maintained between 60 to 70 mm.

What are the Problems Associated with Drain Traps?

Dried-out trap:

The amount of water in the trap dries up if a drain isn’t used for a while (this can happen in guest bathrooms). There will be a release of sewer gas. A dry trap could be the cause of a drain’s foul odor. To fix the water plug, pour water down the drain for a minute.

Slow drains and clogs:

The plumbing trap is a common place for debris to accumulate and cause problems. In addition to soap scum, hair tangles, and food scraps can get trapped in the trap and contribute to the accumulation. These stubborn clogs are often beyond the capabilities of even the most potent sink plunger, requiring the services of a professional plumber.

Poor installation.

When a dishwasher is connected to the kitchen sink’s drain, sewer gasses can leak into the house. Leaks can also develop if the PVC pipe is not attached to the fitting correctly.

Leaks can occur in the plumbing trap like in any other pipe. Check for leaks in the trap if water collects in the cabinet below your sink. Get a plumber to come and replace the trap for you.

Repairing siphon. Plumber in blue uniform is at work in the bathroom
Repairing siphon. Plumber in blue uniform is at work in the bathroom


Floor Trap or Nahni Trap, Gully Trap, P Trap, Q Trap, S Trap, Intercepting Trap, Bottle Trap, and Grease Trap are a few plumbing traps. They come in various materials, including PVC, G.I., etc.

While the above-mentioned plumbing traps see widespread use, the following characteristics and advantages characterize the best plumbing traps:

• Impervious to wear and tear from drops and common household chemicals

• Seal off the sewers to keep out harmful gases, bugs, and parasites.


• Durability

• Low Cost

• Simple Assembly

Installing properly sized and high-quality plumbing traps is essential for maintaining a pest- and odor-free home. Not only is this simple and stress-free to set up, but it also costs less.

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