Toilet Trapway Size: What Is It and Why It Matters? - Glamorous Place (2023)

Incorrectly installing a toilet trapway can damage your plumbing. You will need to do more manual labor or call a plumber to fix it. So, it could mean an extra cost to you.

Toilet trapway size matters so your toilet can flush and function properly. A trapway that is too narrow or too wide can lead to clogging, weak flushing, and other impactful issues.

Let’s look at what a toilet trapway is, why the size matters, and other information worth knowing about your toilet.

Contents hide

1 What Is a Toilet Trapway?

2 Why Does Toilet Trapway Size Matter?

3 Does the Flushing System Impact Trapway Size?

4 What Are the Different Sizes?

5 Toilet Trapway Visual Designs

5.1 Concealed Trapways

5.2 Exposed Trapways

6 What Are the Different Trapway Types?

6.1 S Trapway

6.2 P Trapway

(Video) How Does a Siphon Work? | Ask This Old House

7 How To Find Toilet Trapways

8 How to Unclog a Toilet Trapway

9 Conclusion

What Is a Toilet Trapway?

A toilet trapway connects your toilet to the sewer pipes. You may also know it as an outlet because it’s the small tube that begins at the hole of your toilet bowl.

The trapway is where waste goes and leaves your home to get to the sewer when you flush. Sometimes they are not visible, so you may not have recognized yours. But trapways are crucial to the flushing process.

What the trapway looks like doesn’t matter. The size of the trapway plays a massive role in the functions of a toilet. It can be the difference between an overflowing toilet bowl and a toilet with zero issues.

Why Does Toilet Trapway Size Matter?

There are several functional reasons why toilet trapway size matters.

Your toilet trapway size matters because if it is too narrow, your toilet will constantly clog.

Keep in mind that biological waste isn’t the only contributing factor to a backed-up toilet. Cigarette butts, napkins, tampons, and other garbage can find their way into your toilet. When attempting to flush these objects through a narrow trapway, the small diameter of the trap may not be able to let the objects through.

(Video) HARDEST Toilet Installation Just Got EASIER!

This would inevitably lead to a nasty clog that can cost a lot of money to remedy.

Another reason is a concept called siphoning. A toilet trap should be a particular diameter so that the water flow from the toilet tank will be enough to trigger the siphoning effect. Too big of a trapway would need a wasteful amount of water for a complete flush.

To summarize, trapway size influences:

  • Flushing rate
  • Reliability
  • Size of objects that can be flushed

Does the Flushing System Impact Trapway Size?

Yes. The type of flushing system, siphonic or washdown, determines trapway size you need.

Siphonic Flushing

Siphonic flushing is the most popular type of toilet flushing. This process exploits gravity to suck out the water from the bowl continuously until all the water from the tank runs out.

Eventually, air will enter the system and stop the siphoning process. This is why you hear a gurgling sound when you successfully flush the toilet.

If your trapway is too large, it can affect the siphonic flush and limit its effectiveness.

Washdown Flushing

Washdown flushing also uses gravity, like siphonic flushing. But instead of a vacuum, this method uses weight. It sends wastewater right down as opposed to a curved trapway. This form of flushing utilizes a wider trapway because of the higher water flow used in the design. A narrow trapway will only lead to clogging and won’t work with the toilet hole size that’s optimal for this method.

You’ll typically find these types of flushing in commercial establishments and public spaces. They have a low probability of clogging thanks to the large toilet drain.

What Are the Different Sizes?

With this information in mind, let us look at all the different trapway sizes. This is where it can become a tricky process when repairing a trapway or choosing one for your toilet. Toilet trapways come built into the toilet you buy.

Trapway sizes are very close in size, only ¼ of an inch separating some. With that said, the standard trapway size for home toilets is 2-inches in diameter. Another common trapway diameter is 2⅜ inches. It’s only a bit wider than the standard, but that difference can go a long way in terms of reliability.

This one is the leading size because it makes for a clog-free system. It is still small enough to use siphonic flushing well and fits solid biological waste of most sizes.

The widest available trapway size is a 4-inch diameter, a full 2-inches more than the standard. This diameter is not ideal for siphonic flushing but is perfect for the washdown method.

Of course, there are other sizes than these main three, like 3-inch diameters and 2⅛-inch diameters. Once you consider what flushing system and general trapway size you need, you can determine what toilet would work best for you.

Toilet Trapway Visual Designs

When it comes to visual design, there isn’t a lot to choose from. You can choose between concealed trapways and exposed trapways.

Concealed Trapways

You’ll find these common designs in your home improvement store. The trapway system sits inside the toilet’s housing, away from view. The advantage of this design is that the sides are easier to clean due to the smoother sides which conceal the system.

(Video) Glacier bay Power Flush | stealth technology | extra large trap way to prevent clogs

Exposed Trapways

If you’re looking for a toilet that adds some pizzaz, consider one with an exposed trapway. Instead of hiding the workings of the toilet, these incorporate the trapway into the aesthetic to add visual appeal. The downside is that they are harder to clean because of the curvatures added to the toilet’s body.

What Are the Different Trapway Types?

There are two trapways, an S trap, and a P trap. They both function to create a barrier between your toilet and the sewer. The real difference between them is their shape and effectiveness.

S Trapway

The S-trap looks exactly as the name describes. The water flows along a path that takes the shape of an S. The main issue with this trapway is how it can allow too much water past it and into the sewer. This issue could leave a gap at the mid-line of the trapway.

An air gap creates space for gases to pass through, which can not only lead to odor issues but sanitary ones. These gases can be dangerous and make you and the people in your home sick.

P Trapway

The P trap removes the issues that the S-trap has. By adding more piping, it fixes the issue of excessive water flow. It’s an efficient flushing process that consistently gives way to more water. The water acts as a barrier against gasses. Read more about a P trapway here.

How To Find Toilet Trapways

Toilet trapways tend to come attached to the toilet you purchased. Some toilet designs sell trapways separately in case you need a replacement.

Toilets that come with a specific trapway tend to be built for a certain flushing method. But you can get the individual trapways at most home improvement stores. Or you can buy them from the toilet manufacturers themselves(if you’re having trouble with your flush, see our article ‘Toilet Flushes But Waste Comes Back’).

An example is this toilet trapway from Kohler, that you can buy separately.

How to Unclog a Toilet Trapway

Now you know what toilet trapways are and why their sizes matter. Now, it’s worth learning how to solve a blockage problem caused by improperly flushing the toilet. For instance, you could have expected your home toilet to flush as efficiently as public toilets that use the washdown method.

You don’t need expensive tools to unclog an S-Trap toilet. Grab a plunger and submerge it gently into the bowl. Ensure that the lip of the plunger cup surrounds the base of the trapway. Slowly push the plunger into the trap without any sudden jerking motions. This is will avoid any nasty splashing.

Hopefully, after a few seconds, you’ll see the water receding down the trap. Then, you can attempt to flush the toilet.

If your toilet trapway is clogged with something bigger, like a kid’s toy, a feminine product, or anything else accidentally flushed down the toilet, a plunger might not cut it. You may need to buy a toilet auger.

A toilet auger or toilet snake is designed with flexible metal. This material allows it to snake its way inside the trapway. Insert the toilet snake’s shaft into the trapway. Once it’s all down there, hold the handle with your other hand and turn it continuosly.

You could also push and pull on the handle repeatedly to push down what’s causing the blockage. Finally, you can combine the two motions if you want to ensure that the entire blockage is released.

It’s worth noting that both these methods of unclogging a toilet trapway work for toilets with both S-Traps and P-Traps.


A toilet trapway is an integral part of your toilet. It efficiently flushes down any biological solid waste through the elegant use of gravity.

(Video) How to install a skirted toilet with a sealed trapway

But it isn’t the first thing that comes to mind when homeowners buy a replacement toilet. That’s why it’s essential to know the basic workings of your toilet trapway so you know how to fix any issues that come up when a toilet is misused.


Does toilet trapway size matter? ›

Trapway sizes range from the industry-standard 2-inch diameter up to the industry-leading 2-3/8-inch diameter. The larger the toilet trapway, the better the overall flush performance will be.

How big should the Trapway be in a toilet? ›

The American National Standards Institute sets forth the minimum size requirement for trapways, which is currently at 1.5 inches. Many toilet manufacturers opt for toilet trapways between 1.75 and two inches. This helps to ensure higher flushing performance and peace of mind for homeowners.

What is the Trapway of a toilet? ›

A toilet trap, or trapway, is a curving channel inside the base of a toilet that leads from the hole at the bottom of the bowl to the drainpipe. When a toilet backs up and the clog did not occur in the drainpipe, the stoppage usually exists in the trap.

What toilet has the largest trapway? ›

The Champion® 4 Flushing System has the largest siphonic trapway (2-3/8" diameter) and the largest flush valve (4" diameter) is virtually clog-free, so you'll never have to plunge again. It's packed with innovative features that make it ideal for busy and/or large households.

Should I use 3 inch or 4 inch toilet drain? ›

In new construction, 4-inch drains can be installed from every toilet, or you can run a 3-inch drain line from a toilet to the home's main 4-inch drain pipe -- the line running from the house to the sewer or septic system. Older homes may have only 3-inch drains, so that's what you have to work with.

What toilet height is better? ›

Toilet Height

Standard-height rims are 14- to 15-inches from the floor and should work well for shorter people. If you're taller, consider chair height toilets that have a toilet seat height of 17-inches or more.

How do you measure a trapway? ›

Measuring an S Trap Toilet Waste

Simply measure the distance between the rear wall and the centre of the waste pipe that is exiting through the floor. Back to wall and connector toilets will usually have a measurement range so it can be adjusted to fit different measurements.

How long can a toilet trap arm be? ›

Developed length 6' max. The length of Water closet (toilet) trap arms is measured from the floor flange to the inner edge of it's vent. Developed length shall not exceed 6'.

Does toilet outlet size matter? ›

American Standard Toilets are designed with outlets ranging from 1 3/4” all the way up to an industry leading 2 3/8” outlet. The larger the toilet outlet, the better the overall toilet performance will be.

Which toilet trap is best? ›

P-traps are generally considered by most to be more effective and consistent in maintaining water trap compared to S-traps. Their design makes them less vulnerable to drying out and losing seal: a properly installed P-trap will never lose its water seal.

Do I need a trap for my toilet? ›

All plumbing fixtures need to have a trap. Inside a p-trap is 2-4 inches of standing water. This standing water is called the trap seal. The trap seal is what blocks sewer gas from invading into your home.

What is a toilet skirted trapway? ›

Simply put, a skirted toilet means the toilet has a skirted trapway. A skirted trapway covers up all the bends and curves you see on a standard toilet bowl, with a smooth sleek side that's easier to clean. In most cases, skirted toilets can be installed using the same rough plumbing setup as a standard toilet.

What toilet has the strongest flush? ›

The Kohler pressure-assisted toilet range is one of the best-known ranges of powerful flush toilets. Many models incorporate specially engineered flushing mechanisms and use gravity to provide a more powerful flush using as little as 1.28 gallons of water per flush.

What is the best toilet for not clogging? ›

5 Best Non-Clogging Toilets
  • Best Durable : Woodbridge One-Piece Toilet.
  • Best Anti-Clogging : Kohler's Non-Clogging Toilet.
  • Best For Space Saving : American Standard Non-Clogging Toilet.
  • Best With High-Quality Porcelain : Horow Store's Toilet.
  • Best Water Saver : DeerValley Toilet Bowl.
Feb 16, 2023

What is the best size pipe for a toilet drain? ›

A three-inch pipe is what's used in homes to pipe toilets. The four-inch pipe is used as the building drain under floors or in crawlspaces to transport all the wastewater from a home out to the septic tank or sewer. The four-inch pipe may also be used in a home if it's capturing two or more bathrooms.

What is the most common toilet supply line size? ›

Typically they are 3/8” in diameter, but toilet supply line size can vary in length, usually anywhere from 9” to 20”. Measure for accuracy to ensure you are buying a part that will match your installation.

How many toilets can you put on a 3 inch line? ›

No more than four water closets or bathroom groups shall be installed on a 3" horizontal fixture branch.

Does the height of the toilet matter? ›

These are generally called “comfort height” toilets. A taller toilet is important for people with a number of physical disabilities, including those who suffer from knee injuries, arthritis in their knees or hips, need to transfer from a wheelchair, suffer from neuropathy, and more.

What is the difference between comfort height and chair height toilets? ›

ADA-compliant chair height is a minimum of 17 inches and a maximum of 19 inches from the finished floor to the top of the toilet seat. Standard height toilets are typically 14 to 15 inches in height.

Why would I want an elongated toilet bowl? ›

Elongated bowls are also considered more 'hygienic' in that the larger surface area of the bowl makes is easier for men and children to use with less mess. The longer bowl size is also a requirement for ADA use, and the longer/wider bowl is generally easier to use for those with mobility issues.

What determines the size of the trap on a fixture? ›

Where the tailpiece of a plumbing fixture is larger than that indicated in Table P3201. 7, the trap size shall be the same nominal size as the fixture tailpiece. A trap shall not be larger than the drainage pipe into which the trap discharges. For SI: 1 inch = 25.4 mm, 1 gallon per minute = 3.785 L/m.

How far from the wall should a toilet rough in be? ›

So looking at the toilet, make sure there are at least 15 inches of clearance from the center of the toilet to any adjacent fixture (or wall).

Can you use a 10 inch rough in toilet with a 12 inch? ›

However, even if a toilet is designed for a 10-inch rough-in, you can still install it into a space that has a 12-inch rough-in. Visually, it will appear differently than a toilet installed with the proper rough-in, but it should still function correctly.

What is the minimum size of a trap? ›

No trap or fixture drain shall be less than 1-1/4 inches, except as provided for in Section P904. 5. The fixture drains for water closets, trap standard service sinks and pedestal urinals with integral traps shall not be less than 3 inches.

What happens if trap arm is too short? ›

If the trap arm is too short, waste might splash up into the vent and eventually clog it. A trap arm should be at least two pipe diameters long. For example, if the trap is 11⁄2 inch diameter, the trap arm should be at least 3 inches long.

What is the minimum size trap and trap arm? ›

i. Fixture arm and trap shall be 11/2 inches minimum; vertical drain shall be 2 inches minimum.

What is the difference between a 2 inch and 3 inch toilet? ›

The difference in flushing power between a 2-inch and a 3-inch flush valve can be substantial, and the larger valve can produce a better flush with much less water. There are some great toilets using only 1.28 gallons per flush with a 3-inch flush valve.

Can you vent a toilet with a 2 inch pipe? ›

Toilet Vent Pipe Size? It's typically recommended that you go with a 2" PVC pipe for the vent. This is according to the uniform plumbing code (UPC). It may not be enough, depending on how many fixtures you are trying to run off the vent.

How do I know if my toilet is a 10 or 12 rough? ›

If the old toilet is still there, measure from the center of the capped bolts (on the bottom) to the wall (not the baseboard). There should be 24 inches of clearance from the wall facing the bowl and 15 inches on each side as a guideline. If your measurements are between 11.5 and 12.5 inches, it is a 12-inch rough-in.

What are the different types of toilet trap? ›

There are three common pan types: S-trap, P-trap and skew trap. The trap is the bend in the toilet pipe that gets rid of the waste, and keeps smelly sewer gases from coming up into your bathroom.

What is the most common type of trap in plumbing? ›

In domestic applications, traps are typically U, S, Q, or J – shaped pipe located below or with in a plumbing fixture. The most common of these traps are referred to as a P trap.

What is the difference between S-trap and P-trap toilet? ›

What is a Toilet S-Trap? Unlike an S-trap, a P-trap features a pipe that exits the toilet through the wall. Instead of creating an S shape by going first up and then down, a P-trap creates a P shape by going down, curving up and then proceeding straightly.

How do you fit a toilet trap? ›

A Guide To Installation Of An S-Trap Toilet Pan
  1. Removal of the old toilet.
  2. Finding the S-trap below the toilet pan.
  3. Attaching the mains water and cistern.
  4. Need for a vent.
  5. Connecting directly to the vent stack.
  6. Bring it all together using a wye and a street elbow.
  7. Install the toilet vent adapter.
Jun 30, 2022

What is the difference between skirted and exposed trapway? ›

A concealed trapway toilet has a smooth surface at the back that essentially covers the trapway. A skirted toilet, on the other hand, provide a clean, sleek line from front to back, and from the top of the tank to the floor, making it easy to clean.

What is the difference between a skirted toilet and a regular toilet? ›

A skirted toilet is the same as a regular toilet but with an added apron that goes around to conceal the trap way and create a seamless appearance. Non-skirted toilets have exposed piping and ridges, and are familiar to most people as they are commonly found in most homes as their starter toilets.

Which is better round or elongated toilet? ›

Most people find elongated toilet bowls to be more comfortable, but in a small bathroom, a round bowl can save space. Elongated toilet bowls measure up to 31" from the wall, while round fixtures max out at 28". Because round bowls are less expensive than elongated bowls, they save a few dollars, too.

What are 2 things you should never flush down a toilet? ›

10 Things You Should Never Flush Down Your Toilet
  • Wet Wipes, Baby Wipes, or Any “Flushable” Wipe. ...
  • Paper Towels and Tissues. ...
  • Dental Floss, String, Hair, and Thread. ...
  • Q-Tips, Cotton Balls/Pads, and Feminine Hygiene Products. ...
  • Contact Lenses. ...
  • Medication. ...
  • Cooking Oil, Grease, or Fats. ...
  • Bandages.
Feb 19, 2021

What is 1 thing that should not be flushed down the toilet? ›

Our sewer systems were designed to only transport toilet paper, water and human waste. Which means only toilet paper, water and human waste can be safely flushed down the toilet. Items marketed as “flushable” are regularly found in clogged pipes and broken pumps throughout the sanitary sewer system. Don't flush them.

What is the most powerful American Standard toilet? ›

To verify its power and unmatched performance, the Champion Toilet Collection has been tested and proven by American Standard to flush a bucket of golf balls in a single flush, using 20% less water than conventional toilets.

Can I mix vinegar and baking soda in toilet? ›

Baking soda and vinegar, when mixed together, can form a chemical reaction that looks sort of like an eruption. This chemical reaction can help clear your toilet and any pipe clogs that you might have.

What foods clog toilets? ›

Which Foods Not to Flush
  • Bones and Other Hard Materials. Hard foods, such as bones and fruit pits, take a long time to decompose and are one of the most common causes of food-related plumbing clogs. ...
  • Grease, Fat, and Oil. ...
  • Grains such as oats, barley, and rice can seem small and innocuous at first.
Dec 23, 2020

What makes a toilet flush stronger? ›

You can adjust the float by moving it with your hand and changing its position on the arm through which it connects to the toilet's refill tube. Your toilet should flush stronger now. If not, you will have to call a plumber to diagnose the problem and fix your toilet flush.

What is the best toilet trapway size? ›

The American National Standards Institute sets forth the minimum size requirement for trapways, which is currently at 1.5 inches. Many toilet manufacturers opt for toilet trapways between 1.75 and two inches. This helps to ensure higher flushing performance and peace of mind for homeowners.

Which brand of toilet is most reliable? ›

The 10 Best Toilet Brands to Consider
  1. Kohler. Established in 1893, Kohler is one of the leading plumbing fixture brands in history. ...
  2. American Standard. American Standard sells reliable toilets, among other plumbing fixtures. ...
  3. TOTO. ...
  4. Duravit. ...
  5. Swiss Madison. ...
  6. Gerber. ...
  7. Cotto. ...
  8. Niagara Conservation.
Jan 24, 2023

Do elongated toilets flush better? ›

Elongated bowls may also be slightly easier to use for taller adults and may flush with somewhat more force than round toilets. This might mean they're slightly easier to clean regularly and require fewer “double flushes” to empty the bowl after use.

Does toilet rough-in size matter? ›

An accurate rough-in size ensures there will be enough space between the drainpipe and the wall for the backside of your toilet and the toilet tank of your toilet to fit when installed.

How do I know what size toilet flush valve I need? ›

Look at the flush valve drain opening at the bottom of your tank.
  1. If the opening looks about the size of a baseball or orange, you need a 2″ flapper.
  2. If the opening looks about the size of a softball or grapefruit, you need a 3″ flapper.

Does toilet need a trap? ›

All plumbing fixtures need to have a trap. Inside a p-trap is 2-4 inches of standing water. This standing water is called the trap seal. The trap seal is what blocks sewer gas from invading into your home.

How far away from wall should toilet bowl be? ›

Most codes require at least 15 inches (measured from the center of the toilet) from any side wall or obstruction and not closer than 30 inches center to center to any other sanitary fixture. (The NKBA actually recommends 32 inches.) There should be at least 24 inches of clear space in front of a toilet or bidet.

Are higher or lower toilets better? ›

The higher bowl height can be good for the knees and back and can offer real advantages to taller folks, the elderly and people with mobility problems—these toilets are extremely popular and widely used. But comfort height isn't comfortable for everyone.

What does 12-inch rough in mean for a toilet? ›

Toilet Rough In Dimensions: A toilet's rough-in measurement is the space between the wall behind the toilet and the center of the waste pipe. Standard toilet rough in dimensions are 12 inches but can be anywhere from 10 to 14 inches in some cases.

Is there such thing as an 8 inch rough toilet? ›

We have the toilet 8 inch rough in you need to get the job done right.

How do I choose a toilet flush? ›

To find a top performer, shop at home centers like the Home Depot toilets section with these features in mind.
  1. Tip 1: Compare flush ratings online.
  2. Tip 2: Check for rebates on high-efficiency models.
  3. Tip 3: Get a pressure-assist toilet if a clean bowl using less water is a top priority.
Feb 28, 2023

How do I choose a low flow toilet? ›

Look for models that are labeled as high-efficiency. These toilets will give you the most water and financial savings. And, in some locations in the United States, sizable rebates are available to water utility customers for these toilets. Make sure you get a toilet with the WaterSense label from the EPA.

How do I know if I have a 10 or 12 inch rough in toilet? ›

If the old toilet is still there, measure from the center of the capped bolts (on the bottom) to the wall (not the baseboard). There should be 24 inches of clearance from the wall facing the bowl and 15 inches on each side as a guideline. If your measurements are between 11.5 and 12.5 inches, it is a 12-inch rough-in.


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