J-Trap vs. P-Trap: A Complete Comparison

Talking about plumbing traps is extremely confusing at times. Unless you’re an expert, figuring out the differences between S-traps, U-traps, J-bends, and P-traps is nothing but challenging. Figuring out these differences is important, though, especially since some traps are not legal anymore. That said, the J-traps and P-traps create the most confusion: what is the real difference between those?

The main J-trapP-trap difference is the way the trap couples to the drain and sewer pipe. J-traps feature a captive nut on the short arm, whereas the popular P-traps have removable nuts on both arms. Apart from this, they look and work in the same way.

P-Trap vs. J-Bend: Is There Any Difference?

From a visual standpoint, there is no difference between P-traps and J-traps. They all consist of a vertical pipe section connected to the sink’s tailpiece and a U-bend that connects to the wall drain via a horizontal pipe.

The only difference between the two is that P-traps have two removable nuts, whereas J-traps feature a captive nut on the short arm.

This could seem like nothing, but it makes a big difference. If you have to remove the P-trap for some reason (for instance, if you’re replacing the sink or installing a new flange) and damage the captive nut, you’ll have to replace the entire J-trap. However, you can simply buy a new nut – and save some money – if you’ve broken a P-trap’s nut.

U, P or J: Visual Differences Between Traps

There isn’t much visual difference between U-, P-, and J-traps. They all serve the same purpose, albeit there are some slight differences you should know about.


The U-trap – or U-bend – was invented to solve the clogging and siphoning problems of S-traps. It owes its name to the shape; as you can expect, a U-trap looks exactly like the letter U.

This plumbing trap is characterized by symmetric geometry. Both sides of the bend have the same length, while both pipe connections are positioned either at the top or on the sides. Some U-traps have wye-style fittings, making it easier to connect the sink drain and the trap to the wall outlet without using additional elbows or a sanitary tee.

When installing a U-trap with four couplers, you can use caps on the two you don’t need or attach more than one fixture to the same trap. For instance, you can use such a trap to connect a washing machine and laundry sink or kitchen sink and dishwasher to the same drain.

P- or J-Trap

From a visual standpoint, P-traps and J-traps look alike. Both of them have the U-bend portion the U-trap is famous for, but the U is longer on one side and shorter on the other.

The longer arm links to the fixture’s tailpiece (a vertical pipe), whereas the short arm connects to the wall drain through a 90-degree elbow and a horizontal pipe.

Due to this design, the trap looks like a J before installing it and like a P once it’s installed. Despite the visual aspect, though, there is a slight difference between these two traps. As mentioned above, only the P-trap comes with two removable nuts – a detail that makes all the difference and to which the P-trap owes its popularity.

What Is The Purpose Of P-Traps And J-Bends?

The purpose of all plumbing traps – S-, P-traps, and J-bends alike – is to create a seal between the drain pipe connected to the sewer lines and your home. This seal is needed to prevent sewer gas from leaking into your home.

Sewer gas is a toxic and potentially deadly mix of gases, including hydrogen sulfide, methane, carbon monoxide, esters, ammonia, nitrogen oxides, and sulfur dioxide, among others. All these gases are toxic and have repulsive smells. 

By trapping them out of your house, the plumbing traps not only help keep you and your family healthy but also prevent foul smells from getting inside your home.

6 Common Problems With J-Traps or P-Traps

J-bends and P-traps don’t have many problems. You could go years without ever having to unclog or fix your trap. However, there are a few things you should be aware of when installing one.

Alignment Problems

One of the main things to pay attention to when installing a plumbing trap – or any other pipe, as a matter of fact – is the alignment. If the pipe pieces aren’t perfectly aligned, the nut or coupler won’t seal the connection properly, leading to leaks.

Because J-traps come with captive nuts, they might also use compression washers for a tighter seal. Thus, you should pay attention to align the washers too when tightening the nut.

As a rule of thumb, you should always tighten the trap nuts by hand. Manual tightening ensures a proper seal without leading to over tightening issues. Moreover, you can loosen the nut and realign the trap or washers should you have to.

Clogging Issues 

As mentioned above, U-bend traps rarely clog. However, that doesn’t mean that you can flush anything down the drain. The most common clogging causes include: 

  • Hair: Failing to clean your tub or shower after washing your hair is one of the most common reasons why plumbing traps get clogged. Wet hair strands tend to stick together in clumps. As you wash them down the drain, these clumps can get stuck in the trap and act as a filter for other debris, including soap scum.
  • Grease and oil: While bathroom traps have to deal with hair, your kitchen traps might get clogged due to the grease and cooking oil you’re washing down the drain. When these greasy products get cold, they harden and stick to the pipes. Congealed grease acts as a stopper, blocking the pipes and your trap.
  • Soap: Like grease and oil, soap can also deposit on your trap. Moreover, some soaps react with the minerals in water and create a chalky substance that clings on the trap and blocks it.
  • Mineral deposits: PVC pipes aren’t generally subject to scale deposits, nor do they suffer rust and corrosion. However, minerals can deposit sooner or later, especially if you have hard water in your home. The easiest way to prevent these clogs is by installing a water softener.
  • Foreign objects: Lastly, all foreign objects that get flushed accidentally can cause a blockage. These include jewelry, small toys, larger soap pieces, hair ties, food scraps, etc. That’s why you should use strainer baskets on all drains in your home, regardless if they’re in your bathroom or kitchen.

Water Leaks 

There are two main reasons your plumbing trap might leak. A misalignment is one. The other is a worn-out coupler, nut, or compression washer. Both issues are very easy to fix by simply changing the nut or aligning the trap.

That’s also where the J-trap has a slight disadvantage over the P-trap since you won’t be able to replace its captive nut if it is broken. In this case, you’ll need a new trap.

Gas Leaks

Gas leaks rarely happen when using a P- or J-trap, but you could smell foul odors coming from the fixtures if the trap dries out.

This can happen if you’re not using the fixture for a prolonged period. For instance, the sink trap in your guest bathroom may dry out if you’re not using the bathroom for a while. 

Another reason for dry traps is siphoning. In modern plumbing systems, siphoning rarely occurs. However, if your plumbing system isn’t vented properly, it might suck out the water in the trap and let your home be exposed to sewer gas leaks. The only way to fix it is by re-projecting your plumbing system.


PVC pipes and traps are known for their durability, and breakage rarely occurs. However, the trap could become weak due to chemical clog removers you might use.

When using these corrosive substances too often or improperly, they could attack the PVC surface and create holes in it. The material will become brittle, and it will eventually break.

Physical damage can also happen, especially if you like to store stuff under your kitchen or bathroom sink and don’t pay attention when rummaging through it.

Rust and Corrosion 

Lastly, you should pay attention to rust and corrosion if your house uses metal rather than PVC traps. Metal traps are common in contemporary interiors, especially under the bathroom sink if your bathroom doesn’t have a proper vanity.

While they sport a more flattering look compared to the PVC traps, all-metal fixtures are subject to rust and corrosion. 

5 J-trap Plumbing Tips For Beginners

Wondering how to install, replace, or maintain a J-trap the right way? These plumbing tips for beginners can help you accomplish your mission like a pro.

Avoid Chemical Clog Removers 

Most DIYers believe that chemical clog removers can help them keep their plumbing systems clean and use them even when it’s unnecessary. Don’t become a part of that category. Chemical clog removers can damage your pipes and should only be used sparsely.

If you’re dealing with a clog, try snaking the drain first and see if it works. If the water doesn’t drain, take off the trap and clean it. As a last resort, use chemicals to dissolve a clog that’s further down the drain and that you can’t reach or remove with a snake.

Clean Your Traps Regularly

Maintenance is key to a perfectly functioning plumbing system. Don’t wait for a flood before cleaning your plumbing traps. You should check and clean them at least once a year if the system is new or about once every six months if you have an older plumbing system.

Loosen the Fittings with Heat 

Do you have a metal J-trap and can’t remove it due to a stuck nut? Loosen the fitting with heat. A blow torch should help the metal expand and make it easier to turn the nut and untighten it.

Replace the Washers Before Reinstalling the Trap

Another sound piece of advice is to remove the old washers and replace them with new ones each time you’re taking off the trap. This includes the scheduled maintenance or any other work you might do. In this way, you won’t have to worry about leaks.

Always Tighten the Plastic Nuts By Hand

As a makeshift plumber, you may think that the only way to tighten a fitting properly is with a pair of pliers or a wrench. However, these tools would do nothing but help you overtighten a plastic nut. Not only will the nut be harder to remove, but it could also crack or break.

Thomas Crapper: Founder of U-Trap

Plumbing traps have revolutionized drain systems around the world since their invention back in 1775. Back then, Alexander Cunning invented the now old-fashioned S-trap.

While this trap revolutionized plumbing, it had (and still has) one big problem: the water trapped inside it is easily siphoned out, letting the trap dry. When this happens, the trap ceases to do what it’s supposed to do, and it doesn’t trap sewer gases anymore.

Another big problem with S-traps is that they get clogged easily. That’s why the U-trap, invented by Thomas Crapper in 1880, brought a new revolution when it began to replace the S-trap.

The main difference between the two is the way they connect to the sewer pipe. While the S-trap connects to a pipe in the floor, the U-bend traps (J- and P-traps) connect to a drain in the wall via a horizontal length of pipe.

This layout solves all siphoning problems, so you won’t have to worry about the trap drying out – unless it’s a trap in a guest bathroom that you rarely use.

In addition to the now popular U-trap, Thomas Crapper also held three other patents in toilet improvement. Among them, we can mention the floating ballcock, an essential element for flushing. And, as you can imagine, Crapper’s surname and his association with lavatories gave birth to the popular slang we all use nowadays when referring to solid bodily waste.

Frequently Asked Questions

The difference between P-traps and J-traps should be clear now, but you may still have questions. Check out the answers below.

How much room do you need for P-trap?

According to the International Residential Code and the Universal Plumbing Code, the distance between the sink drain and P-trap entrance must be 24 inches or less. With this in mind, you need about 26 inches of vertical space under your sink to install a P-trap. The codes don’t stipulate any length for the horizontal pipe connecting the trap to the wall drain.

Is it wrong to connect multiple J-bends (traps) together?

You should never connect multiple J-bends together; such a configuration almost always leads to clogs due to too much up-and-down under the sink. If you can’t align the sink drain with the wall drain pipe, use 90-degree elbows or 45-degree angles to divert the pipe as needed.

Does my p-trap have to be straight?

No, the P-trap doesn’t have to be straight. In fact, more often than not, the horizontal section is diverted to align perfectly with the wall drain. This doesn’t affect the trap’s functionality, nor will it lead to clogs, as long as you use elbows and angles to divert the pipe. As mentioned above, you should never install multiple traps on the same line.


J-trap and P-trap terms are often used interchangeably, but the two trap types are actually different. Sure, the differences are so small that you could easily use either one and achieve the same result. As a general rule, though, P-traps are more practical thanks to the removable nuts used on both ends.

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