The Ultimate Toilet Trap Guide: P-Trap vs S-Trap vs Skew Trap

Not all toilets are created equal - and we're not just talking about the shape, design or different combinations of materials used in their construction.

Toilet suites also differ based on their functional features. For example; the path that water (and any type of waste) follows from the toilet bowl to the sewer is different too.

Back in the old days, installing a toilet had numerous complications. These included a series of foul-smelling and sometimes dangerous gasses exiting the sewer through the toilet pipes.

This obviously made living spaces very unpleasant to be in. Occasionally, even cockroaches, rats and other undesirable creatures could find their way to the bathroom through the internal parts of the toilet.

This created a challenge for toilet designers, makers, and installation personnel. How could they keep homes free of these nasty odours and visitors while still achieving the primary goal of a toilet (the quick and effective removal of any biological waste)?

This problem was solved thanks to the invention of the trap, which redefined toilets as we know them.

In this toilet trap guide, we will first explain what a trap actually is and does. With that out of the way, we will help you solve one of the doubts you are probably losing your sleep. P-trap vs S-trap vs skew trap: how to pick the right one?

What is a Toilet Trap? 

Traps are a common feature of any plumbing fixture, whether we're talking about a kitchen sink, a bath tub, or a back-to-wall toilet suite.

They have a critical function: using water to create a barrier between your living space and the sewer. This water barrier is referred to as a trap seal. 

Its goal is to prevent various foul-smelling sewer gasses (such as methane, ammonia, nitrogen, or sulphur dioxide) from finding their way back to your home by passing through the drainpipe.

More specifically, we use the expression toilet trap to refer to the curved channel that begins at the bottom of your toilet bowl and ends in the drainpipe. When you flush, the water flows down the trap and right into your plumbing.

When traps dry up, problems can become even more severe than foul odours. Some gasses (such as carbon monoxide) can be very toxic. 

As if that wasn't enough, vermin may find their way up to your bathroom and living space. These are two things you definitely want to avoid at all costs.

Traps also serve another function. They work as a filter for debris (or other objects) that could prevent water from flowing through your sewage pipes.

What is a Toilet Set-Out? 

The toilet set-out is another essential element you should consider when renovating your bathroom and installing a new toilet. 

It refers to the distance between the waste pipe's centre and the floor (if you're using a P-Trap) or the finished wall (if you're using an S-trap).

It's crucial to take note of set-out measurements when looking for a new toilet to install. You need to make sure that there is a match between the new toilet's set-out and the current plumbing.

Set-out measurements usually vary based on how old your home is. In most modern homes, the set-out is generally between 140mm and 165mm, allowing most toilet suites to be installed.

Now that you understand how traps work, it's time to take a more detailed look at the various types of toilet traps available on the market.

What Are the Different Types of Toilet Traps?

What is a Toilet P-Trap? 

The name of this toilet trap obviously comes from its unique S-like shape. 

It usually features a pipe that goes straight through the floor from the toilet below. That's why it's typically used when installing a toilet on the ground floor.

An S-trap also takes more space around the waste outlet than other traps. Its set-out is the distance between the wall and the centre of the pipe that penetrates the floor.

This type of trap consists of two pipes tied together to allow the water (and any other type of waste) to go down the first pipe and then into the second one.

The main reason why S-traps are very frequent is that they are the oldest type of trap that made it to the market. This has its downsides, though, as their design may be outdated for many modern homes.

On top of that, S-traps are also more likely to siphon dry up and cause the water level to drop. This makes it easier for undesired odours to find their way into your rooms.

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. 

Its specific form makes it ideal for wall-hung toilets. It is also a good pick for toilets located on top floors.

This type of trap is more innovative than an S-traps, and it's deemed more reliable and effective when it comes to maintaining enough water in the toilet. 

This means that a P-trap is less likely to dry and let undesirable odours reach your bathroom by losing its water seal.

The only situation in which this may happen is when P-traps are not installed correctly by a competent worker. That's why selecting fully licensed plumbers with considerable experience is crucial when you're planning to use a P-trap for your new toilet.

In general, whether or not you can use a p-trap depends on the distance between the centre of the toilet bowl and your wall.

What is a Toilet Skew Trap?

Suppose the conditions are unsuitable for installing either an S-trap or a P-trap.

In that case, a convenient solution is installing a so-called skew trap. This type of trap only needs a small amount of water to fulfil its purpose.

When using a skew trap, water proceeds into the sidewall. Not the floor (as in a S-trap) or the wall behind the toilet (as in a P-trap).

Skew traps are not common nowadays, but their installation is less expensive and takes much less work than mounting the other two trap types.

Generally, you should consider installing a skew trap when you have limited space to install your toilet or face other installation restrictions.

Contact The Sink Warehouse: Australia's Bathroom Experts

Choosing what type of trap to install when renovating your bathroom and installing a new toilet can be a complicated dilemma without the right expertise or guidance.

Things like the current plumbing, the available space and the location of your bathroom must be simultaneously considered to avoid choosing a toilet trap that doesn't fit your specific needs.

Without the assistance of an expert, there is a severe risk of dealing with unexpected problems in the future. 

When renovating your bathroom, there's nothing worse than making a considerable investment in your new toilet and then having to incur additional costs to fix planning mistakes.

The Sink Warehouse has been helping households in Australia with renovation and installation decisions since 1994.

Visit your local store or call 1300 301 000 to receive a personalised evaluation and all the information you need to make the proper decision based on your current situation and plans.