The choice of a toilet is one of the most important yet overlooked decisions in any bathroom project. Not only is it somewhere you’ll spend a bit of time, it’s also an element that can have an out sized affect on the layout of the bathroom.

Before you choose a suite based on aesthetics, flush technology or seat features, you first need to understand how the toilet will connect to your plumbing – particularly your waste pipes.

Let’s break down Australia’s most common toilet traps – S-traps, P-traps and skew traps – to help you understand how the relevant trap may affect your choice of toilet, so you can undertake your bathroom project with total confidence.

Understanding toilet traps and waste outlets

A toilet trap is the bent section of pipe that sits behind or beneath the toilet pan. Its job is to use water to form a liquid ‘plug’ that prevents smells and sewer gases from moving back up the pipe and into your bathroom.

In Australia toilet traps come in three main forms:

S-trap: floor waste

As the waste pipe leaves the pan it forms a sideways ‘S’ shape that exits vertically down through the bathroom floor.

S-trap toilets are standard for Australian homes built before 2000, with the waste plumbing often concreted in.

P-trap: wall waste

As the waste pipe leaves the pan it forms a sideways ‘P’ shape that exits horizontally through the back wall.

In the last few years P-trap toilets have become more popular, as they offer a little more flexibility: wall waste pipes are easier to access and allow for the installation of wall-hung toilets and concealed cisterns.

Skew trap: side waste

After the trap, the waste pipe protrudes from the left or right side of the toilet at a 45-90° angle and exits through a rear or side wall.

Skew traps are reserved for renovations when a toilet needs to be placed in a particularly tight spot or somewhere that doesn’t align with an existing waste outlet.

Understanding set-out distance (and how to measure it)

To choose the right toilet suite you also need to know the set-out. This measurement, also called rough‑in, tells you exactly where the toilet’s trap connects with your home’s waste outlet.

Precision matters with set-out measurements, as even a slight miscalculation can mean your pan won’t sit flush with the waste pipe, which can lead to costly fixes (though some issues have simple fixes like adjustable toilet connectors).

With that in mind, here’s how to measure the set-out for different types of traps:

• S-Trap: Measure the distance from the finished rear wall (inc. tiles) to the centre of the waste outlet in the floor.
• P-Trap: Measuring the height from the finished floor to the centre of the waste pipe in the wall.

For newer homes the set-out should be one of a handful of standard measurements (140-165mm for S-trap, 180-230mm for P-trap). But if your home was built before standards were put in place, you may have a non-standard set-out.

Skew traps are a little different, as they often feature adjustable or flexible connectors that are less dependent on precise measurements.

Matching plumbing layouts to toilet designs

Once you’ve identified your trap type and measured your set-out, you’re ready to shop toilet suites. Here’s a rundown of which suites work best with which traps:

• Standard suites: Either S-trap or P-trap will work. If you’re replacing a toilet, ensure the new suite has the same trap as the old one.
• Back-to-wall toilets: These suites conceal trap connections completely against the wall for a sleek look, space maximisation and easy cleaning. P-traps typically work best here, although S-traps can too if the floor waste is in the right spot. 
• Wall-hung toilets and in-wall cisterns: If you want to add style, reduce clutter and minimise cleaning, you can elevate the toilet off the floor and/or hide the cistern in the wall. A P-trap configuration will be required.
• Close-coupled and skew trap: These are practical alternatives when space is tight or when wall/floor waste positions are set, allowing you to reposition your toilet without moving the underlying plumbing.

Ready to shop for your new toilet?

Whether you’re building a new home or undertaking a renovation, understanding trap types and set-out measurements is your first step to finding the right toilet for your bathroom project.

Shop our comprehensive range of suites today, or if you’re looking for inspiration, check out our list of Australia’s 5 best toilets and our DIY installation toilet installation guide. 

Our team is also here to support you through the whole process, with expert, pressure-free advice whenever you need a helping hand. Just reach out.