Exposed vs. Concealed Trapways: Main Differences
Though it probably doesn’t cross your mind often, a crucial element of your toilet is its trapway or siphon outlet. Trapways can be concealed or exposed, and the distinction lies in their drain pipe design. The drain pipe of an exposed trapway is clearly visible, but a concealed siphon outlet is hidden.
But that’s not all! Beyond appearance, the two types of siphon outlets differ in ease of cleaning and maintenance. Whether concealed or exposed, all trapways perform the same job: facilitating the movement of wastewater to the sewer or septic system.
Ready to learn about toilet trapways and their functions? Keep reading to discover everything you need to know about this important toilet component.
Key Points
- Trapways, also known as siphon outlets, direct waste from your toilet bowl into the municipal sewer or your septic tank. They also prevent sewer gases from entering your home.
- Trapways come in three different designs. They do not affect toilet function, but they’re a great chance to show off your personal style! Exposed trapways are perfect for traditional bathroom designs, while concealed and skirted designs are ideal for modern bathrooms.
- Trapway diameters can range from 1¾ to 2⅜ inches, with larger diameters reducing the risk of clogs and providing maximum flushing power. Aim to choose a trapway with a diameter at or above the industry standard of 2 inches.
- An empty trapway can allow sewer gases to escape into your bathroom, so it’s important to address this issue immediately. Clogs, cracks, faulty tank components, and blocked plumbing vents can all prevent a trapway from staying filled.
What is a Trapway?
Also known as a siphon outlet, the trapway is the curved pipe inside the base of your toilet. This pipe is located at the back of your toilet and connects your toilet bowl to the sewer line. When you flush the toilet, water and waste flow through the siphon outlet and out of your home. There are three types of trapways: exposed, concealed, and skirted. You can also choose from several different trapway sizes. Each design and size has unique pros and cons, which affect things like bathroom aesthetics, ease of cleaning, and ability to effectively remove waste.
Did you know? Wondering about skirted trapways? They’re technically a variation of concealed trapways. This type provides an ultra-clean look by hiding both the trapway and bolt caps. The smooth surface makes sanitization a breeze!
Functions of a Trapway
Now that you know what a trapway is, what are the functions of this vital component of your toilet? Let’s find out.
Smooths the Flow of Waste
The primary function of a trapway is to allow a smooth passage of wastewater from the toilet bowl to the sewage line. But how does this happen?
In most toilets, when the bowl fills during a flush, gravity forces water into the trapway. When the water level rises to the highest point of the trapway, a siphon effect is created. This suction pulls waste and water out of the bowl, resulting in a powerful and efficient flush!
Helps Prevent Clogs
Trapways are designed to minimize toilet clogs by providing waste with a smooth and unobstructed pathway out of the bowl. Their size allows them to effectively handle waste, while their curved shape helps them trap objects (as the name suggests) that could otherwise travel deeper into the plumbing system and cause serious blockages.
Keeps Sewer Gases Away
Siphon outlets also help keep smelly and noxious sewer gases out of your bathroom. They are designed to retain a small amount of water after every flush, which acts as a seal and prevents sewer gases from entering the toilet bowl. That’s right—you have your trapway to thank for an odor-free bathroom!
Adds Visual Appeal
Trapways are unique as a toilet component, as they are both functional and ornate. Whatever your aesthetic preference, a trapway can add the visual appeal to take your bathroom design to the next level!
Exposed trapways incorporate exciting curves, while concealed and skirted trapways keep things sleek and minimalistic. Have fun choosing the style that ties your bathroom’s look together.
Typical Trapway Sizes
When it comes to trapways, size matters! They can measure anywhere between 1¾ inch to 2⅜ inches in diameter. The industry standard dictates that trapways, regardless of design, should be at least 2 inches in diameter to enable optimal flushing and clog-free performance. The most effective toilet models feature a trapway diameter of 2⅜ inches.
Exposed vs. Concealed Trapway: What’s the Difference?
Exposed and concealed trapways serve the same function, which is to allow waste to leave your toilet bowl and make its way to the municipal sewer system or your home’s septic tank. Even so, the two types have some key differences. If you’re in the market for a new toilet, you may be wondering which type to choose. 
The table below will give you a quick rundown of the differences between exposed and concealed siphon outlets so you can decide which works best for your situation.
Now that you have a basic understanding of the difference between exposed and concealed trapways, let’s dive further into their individual designs.
Exposed Trapway Design
As the name suggests, an exposed trapway is visible. This means the curves of the drain pipe can be seen along the side of your toilet. This type of trapway is common in standard toilets and usually features bolt caps.
As you can see in the photos, an exposed trapway features a curvy, S-shaped pipe. Depending on your style preferences, these curves can add visual interest and elegance to your bathroom. The exposed crevices of this design can collect dirt and grime, however, so regular and thorough cleaning is required to maintain its appearance.
Concealed Trapway Design
In a concealed trapway, the S-shaped pipe is hidden away. No visible tube runs alongside the toilet in this design—instead, it incorporates sleek vertical lines. Overall, a concealed trapway is common in contemporary toilet designs.
The photos above show the smooth sides of a few toilets featuring concealed trapways. As you can see, there are no curves or S-shaped outlines.
Exposed vs. Concealed Trapway: Which Should I Choose?
So, is a toilet with an exposed or concealed trapway the right choice for your bathroom? There are a few things you need to think about to answer this question! Let’s run through a list of pros and cons for each type.
Exposed Trapway Pros
- Affordability & availability: This siphon outlet type is typically featured on the most budget-friendly toilet models. A wide variety of sizes and styles are readily available.
- Classic aesthetic: If you’re going for a traditional bathroom design with vintage charm, look no further than a toilet with an exposed trapway!
- Easier to inspect: Because the trapway is visible, routine external inspection is much easier with this type. You can easily detect cracks, leaks, and other issues with a simple visual inspection.
- Simple component repairs: Bolts and hardware are visible and easily accessible on toilets with exposed trapways. This makes repairs to these components quicker and less complicated.
Exposed Trapway Cons
- Harder to clean: The curves of an exposed trapway make it a haven for dust, dirt, and other bathroom grime. More effort is required to keep this type clean.
- Less sleek appearance: If you are aiming for a more modern or minimalist bathroom aesthetic, you may find the twists of an exposed trapway too intricate for your liking.
- Can appear bulkier: If you’re working with a small bathroom space, you may find that the arches and bends of an exposed trapway look bulky compared to their concealed counterparts.
Concealed Trapway Pros
- Sleek, modern design: Those hoping to achieve a modern, streamlined aesthetic are often drawn to the straight lines of this type. Skirted trapways take this even further by also keeping the bolts out of sight, resulting in a clean, smooth look.
- Easier to clean: With no ridges or crevices for grime to accumulate, cleaning this trapway type couldn’t be easier. It’s as simple as wiping down a smooth, flat countertop.
- Makes smaller spaces appear larger: The slim lines associated with this type can make a toilet appear more compact, creating a more spacious feel for smaller bathrooms.
- Higher perceived quality: Concealed trapways are often found on high-end toilet models, upping the luxury factor in your bathroom.
Concealed Trapway Cons
- More expensive: That luxurious appearance comes with a price! Toilet models with this trapway type are often more expensive due to the additional materials and craftsmanship required.
- More challenging to install: Accessing the bolts of a new toilet and securing it to the floor can be more difficult with this type.
- Less widely available. Though the popularity of this type is growing, available models are still somewhat limited compared to exposed trapways—especially in lower price ranges.
No Water in the Trapway: Troubleshooting
Enough water to cover the opening of the trapway should always remain after flushing to keep sewer gases out of your home. An empty trapway will eventually allow those smelly and dangerous compounds to escape into your bathroom, resulting in unpleasant odors and even potential health problems. Scary!
The good news? Fixing this issue is usually easy and straightforward. If evaporation or lack of recent use is the cause of your toilet’s empty trapway, all you have to do is add some water to your toilet bowl. Simply pour in enough water to cover the trapway’s opening.
If this doesn’t fix your issue, or if your toilet consistently fails to refill the trapway sufficiently, you may need to dive a little deeper. Here are a few potential causes:
- Toilet clogs: A clogged toilet can prevent a toilet from flushing and refilling properly, leaving you stuck with an empty trapway. This issue is usually easily fixable with the help of a plunger. Check out our guide on DIY solutions to toilet clogs for more information.
- Faulty flapper or fill valve: A misaligned flapper or malfunctioning fill valve may not allow enough water to refill the bowl after a flush, leading to a dry trapway. Checking and replacing these parts is easy with our DIY guide.
- Toilet bowl or trapway cracks: A crack in your toilet’s porcelain can allow water to leak out, preventing the trapway from remaining full. Inspect the toilet bowl and trapway for visible cracks and leaks. If you find any, you will likely need to replace the toilet or affected part. In the meantime, you can try to seal the leak with a waterproof epoxy.
- Leaks around the trapway: If you find water pooling around the base of your toilet, your toilet may not be properly secured to the floor. You can try tightening the mounting bolts that keep it in place, but be careful not to overtighten. If the issue persists, there may be a problem with the toilet’s wax ring. Check out our DIY master guide for information on replacing a wax ring.
- Blocked plumbing vents: Negative air pressure and suction in your plumbing system can siphon water out of your toilet bowl, resulting in a trapway that won’t stay filled. This can be caused by blocked plumbing vents. Check out the section on fixing blocked vents in our comprehensive guide on maintaining the proper water level in a toilet.
Bottom Line
We hope you’ve learned something new about toilet trapways today! Also known as siphon outlets, trapways are the indispensable link between your bathroom and the outside world, removing waste so you can enjoy a clean and sanitary home.
Believe it or not, they can be functional and fashionable! If you’re shopping for a new toilet, you can incorporate your personal style into your bathroom with your trapway design choice. For vintage and traditional bathrooms, consider an exposed trapway. If you prefer a minimalist look, a concealed or skirted trapway may be the right choice.
Your trapway should always remain filled with enough water to keep sewer gases at bay—but if it runs dry, don’t panic! This useful guide can flush away your worries by helping you restore your toilet to working order.