What Are Dual Flush Toilets? | Everything Explained

You were at a friend’s house and visited their cloakroom. After you were done on the loo, you stand up to flush and are faced with a pair of buttons instead of a lever. What is that? You are using a dual flush toilet.

In this post, I’ll explain what a dual flush toilet is, how it works, look over its pros and cons as well as answer some common questions on the topic.

Let’s dive in!

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What Is A Dual Flush Toilet?

There are a pair of buttons located on the top of the cistern. Press the first button, and you use less than three litres of water to wash down any fluids in the bowl. For solids, hit the other button, and it will release all six litres for thorough rinsing of the bowl.

A dual-flush toilet represents the second generation of low-flow toilets. While traditional and the first low-flow toilets used a single lever to operate, the dual flush toilet gives you the option to use even less water for a quick flush.

Before water-saving toilets were introduced in the late twentieth century, a single flush of an older toilet wasted up to 25 litres of water. With one person visiting the loo up to seven times a day, that’s 175 litres washed through the sewer pipes to move about two litres of waste. That’s a lot of water wasted!

What Is A Dual Flush Toilet?

How do dual flush toilets get it to go down?

The most noticeable difference between an old lever-flush toilet and the modern dual-flush is that you see very little water sitting in the bowl. If there is no water for the solids to swim in, how does it end up going down?

The old style of toilets used a narrow waste drain and the pressure of 25 litres of water to force solid waste through a trap underneath the bowl. When low-flow toilets came on the market, adjustments had to be made to make sure that every flush resulted in a clean bowl.

The size of the waste pipe increased by half and jet technology was used to help the water power-wash the sides of the bowl to create a stronger vortex. Basically, the force of the rushing water and the escape hatch both increased.

The Cost of Installing a Dual Flush Toilet

The problem that most homeowners encounter when upgrading to a low-flow or dual flush toilet is that not every toilet is built to the same standard. A recent study found that more than 8% of the new-style toilets leaked.

The water lost through bad flush valves exceeded the total amount of water saved in properly functioning toilets. For this reason, you will want to do your research and invest in a high-performance loo.

Prices for a dual-flush toilet range from £150 to £500. The price does not necessarily coincide with improved performance. The higher-priced versions are more for looks than function.

You won’t need to do any retrofits to your bathroom to switch out the toilet. However, some of these toilets use a pump-assist to create the force needed for a clean flush. You may need an electrician to add power to the bathroom.

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How does a dual flush toilet button work?

In a dual flush toilet, each button uses a push rod to pull the flush valve up to release the water. The first button raises it just enough to let three litres into the bowl. The second button lifts the valve higher allowing extra time for the full six litres to wash into the bowl.

Once the valve is reseated, the fill valve stays open until a float located inside the cistern shuts it off.

As far as your toddler needs to know–they just push down on either button until you hear the rush of the water.

Some buttons are harder to press than others. If you have young children or are designing a bathroom for a senior, you might want to test the button in the showroom before buying.

How does a dual flush toilet button work?

What Are the Benefits of Dual Flush Toilets?

The pros associated with upgrading to a dual-flush toilet include:

  • Reduce your whole home water usage by 30% per day compared to a traditional high-flow toilet.
  • Maximise water conservation by using the liquid-only flush button.
  • Modern engineering improved the shape of the bowl for better disposal of solid waste.
  • Costs the same to purchase and install as a traditional toilet.

What Are the Problems with Dual Flush Toilets?

Unfortunately, when low-flow toilets were mandated in Europe and America in the late 20th century, toilet technology did not improve at the same time. Dual flush toilets have a reputation for leaking and clogging.

The flush valve seal often gets dirty or becomes brittle and no longer functions, allowing water to constantly flow down the drain.

Because you are using up to 75% less water to flush down solids, older sewer systems struggle to keep it all moving. Homes with dual flush and low-flow toilets are more likely to have a huge clog in the waste pipe connecting to city services.

There are a few toilet manufacturers that have built a reliable product. Toto from Japan has the best reputation, but you can’t always find them locally available. You will need to do your own research to make sure that you are not buying a bad toilet.

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What happens if you push both buttons on a dual flush toilet?

Pressing both buttons on the dual flush toilet gets the same result as just pushing on the larger button.

It releases a maximum of six litres of water to rinse the bowl.  It will not give you extra pressure or more water, because you already emptied the cistern.

If you need to flush again, you’ll have to wait for the cistern to refill before hitting the big button again.

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Final Thoughts…

There you have it! Everything you need to know about dual flush toilets.

While initially, dual flush toilets may not have been the perfect answer to solve water wasting woes, newer more modern models along with up-to-date plumbing are far better and can save a significant amount of water. Just make sure you’re buying a well-made model to prevent leaks. Helping your water bill and the planet at large!

So, will you install a dual flush toilet in your new bathroom?


Michael R

Michael is a KBB designer from the UK. He's been designing and project managing new Kitchen, Bedroom and Bathroom installations for over eight years now, and before that, he was an electrician and part of a KBB fitting team. He created The Bathroom Blueprint in early 2020.