Toilet With Sink On Top | Pros, Cons & Advice

Are you looking for a way to squeeze in a toilet and sink into a small bathroom or even a cloakroom under the stairs? Have you ever seen a toilet with a sink on top? They are popular in tiny apartments across Japan and could be the answer to your small bathroom needs.

In this post, I’ll explain what a toilet with a sink on top is, how it works and its pros and cons as well as answer some popular questions about the topic.

Let’s get into it!

What Is A Toilet With Sink On Top (Toilet Sink Combo)?

A toilet with a sink on top (sometimes called a toilet tank sink, 2-in-1 toilet and sink, or a toilet sink combo) is exactly as it sounds. It is a close-coupled toilet where there is a small sink on top of the cistern (toilet tank). Designed to fit in very small spaces, the basin and taps replace the top of the toilet cistern.

Once you are done with the loo, close the lid and flush. Wash your hands while the toilet refills. You must reach over the bowl to access the small basin.

These 2-in-1 toilet sinks work best for cloakrooms hidden under the stairs or in tiny closets where you have just enough room for a toilet and nothing else. They can also be a great option for caravans or narrowboats.

All the pipes needed for the toilet and sink enter and leave the room at the same place, saving valuable square metres.

You can find a toilet sink as an aftermarket addition to an existing toilet or as a complete unit. The add-on toilet sink can be found for less than £90, and you can install it yourself in just an hour with a few basic tools and a little muscle.

If you want to buy the complete unit, expect to spend about £300. That is about twice the cost of a traditional toilet, but similar to the price of a toilet and basin.

Toilet with sink on top 2in1 toilet sink
Toilet sink combo

How do toilets with sinks on top work?

A toilet with a sink on top works by using the drain in the sink bowl to fill up the cistern for the toilet. The water used to wash your hands is just as clean as the water in any other basin in your home. The water does not go through the toilet tank or bowl first.

The less expensive options connect the cold water supply to the toilet to the tap for the sink. When you flush, the valve opens to start filling the tank and bowl with fresh water.

The water is first diverted to the sink spout, so you can wash your hands while the toilet fills. The water flows down the basin and into the waste pipe that fills the toilet. Once the tank reaches the proper level, the valve inside closes and the water shuts off.

Other (typically more expensive) models offer an all-in-one tap that is directly connected to the cold and hot water supply through pipes plumbed through the bottom of the tank. You can turn on the sink tap at any time and adjust the temperature.

Like the other type, the water flows down the waste and directly into the toilet tank and bowl.  The toilet will not overfill, as it is designed to always maintain the same water level.

Some small basins are formed to hold a bar of soap or a small bottle of liquid soap.

Pros Of A Toilet Sink Combo

  • Perfect Fit in a Tiny Spot: When adding an extra bathroom in your small city flat or tiny house, the toilet with a sink on top makes it possible to fit two pieces where only one can stand.

  • Adding an Extra Toilet for the Family: Finally, you don’t have to wait in the hall for the one bathroom to be open. Even a tiny toilet and sink combo under the stairs is awesome when the need is great.

  • No Extra Plumbing Needed: You will only need to run pipes to a single location when installing a toilet sink. Fewer pipes equal less labour and more savings.

Cons Of A Toilet Sink Combo

  • A Very Small Sink: The basin on top of the toilet is just big enough to wash your hands quickly. You would struggle to even rinse a pair of socks in it.

  • Possibly No Hot Water: If you opt for the aftermarket toilet sink, it will only have a connection for cold water. This is not a great way to properly sanitise your hands after using the toilet.

  • Awkward Design: If you are taller, a toilet sink will seem very short. The bowl might knock your knees backwards. And if you suffer from back aches, reaching for the basin will not be comfortable. It is not an accessible option for everyone.

  • Waste Sits in the Toilet: Whatever you wash down the drain of the basin flows into the toilet tank and eventually the toilet bowl. You might notice cloudy water that still has soap suds. The water in your toilet may not always look clear and clean.

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Is Toilet Tank Sink Water Clean?

Yes, a toilet sink uses perfectly clean water to wash your hands before entering the toilet tank or bowl. You can drink from your toilet sink, just as with any other tap in your home.

What may not look clean is the water in the toilet bowl. Your used handwashing water flows down into the toilet. If it is done with its flush and fill cycle, suds and dirt will remain in the bowl.

Can you add a sink to an existing toilet?

Yes, the two most popular toilet sink add-ons are the SinkPositive and SinkTwice. They price at less than £100 and will fit a variety of toilet tops. They have a sliding design that lets you expand or shrink the top for a secure fit.

These options divert the cold water supply that runs to the toilet and first sends it to the sink. When you flush, the water valve opens. You can wash your hands while the toilet fills.

For today’s water-saving toilets, that gives you about a minute of running cold water to get clean. On older toilets, your basin may run up to five minutes as the water is also used to fill the cistern on the toilet.

Unfortunately, the SinkPositive and SinkTwice models do not connect hot water to the toilet sink. So it will just be a cold water hand wash.

Final Thoughts…

There you have it! Everything you need to know about the toilet sink combo.

While it may not be the most practical way to wash your hands after visiting the bathroom it can be a great space saver and the perfect way to fit in an extra toilet in a small space. As well, it’s a nice way to save water and help out our environment.


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.