Save Water And Money With A Toilet Sink Combo

Saving Water And Money With A Toilet Sink Combo

Toilet Sink Combo

Toilet Sink Combo – Revisiting An Old Japanese Restroom Concept

You should have seen the small restroom in a Japanese home, if you have ever visited one before. Usually it is a small separate cubicle, with only enough space for a toilet and movement.

Inside the little cubicle, there’s a ventilation fan on a wall and a toilet roll holder next to the toilet. The ventilation fan is there to help exhaust the odor besides facilitating air circulation. Which is necessary given the small space.

Some will have a small sink next to or behind the toilet. And it’s not unusual if you see a toilet sink combo unit, with the sink mounted on top of the toilet tank. If you find this toilet and sink in one design interesting, you are late for the party. This toilet sink combo design has been commonplace in Japan since the 1950s.

The Japanese are well known for their innovative use of small spaces. And this creativity was born out of circumstances. Being one of the world’s most expensive real estate after the war, innovation is not an option. You just have to make good use of every square inch available. Including the air spaces.

The Benefits Of Toilet Tank Sink

Leaving space constraint aside. There are several benefits you can reap from this tank sink combo unit. Saving water is a good enough reason you should consider.

Instead of using clean drinking water to fill up the toilet tank for flushing, use used water. That is the water you used to wash your hands with after using the toilet.

Your toilet will work the same way with a sink sat on top of the tank. You still get the same flushing power. The difference is in the way it fills up the toilet tank after every flush.

The design is such that water from the supply line channels through the faucet for you to wash your hands. And then drained out through the sink drain and into the tank. The water will keep flowing to fill up the tank, until it gets shut off by the float.

This way water is not wasted. Compare to the usual when you have to wash your hands on a separate sink with clean water. And it adds up to more water used for each visit to the toilet.

And because the refill is automatic, you don’t have to turn on any faucet knob or handle. So there is no risk of contamination through contact, making your toilet a lot more hygienic.

More important is, with this toilet sink combo you are helping to conserve water. And playing your part for a greener environment.

What Are The Options Out There?

“I really love my existing toilet and I also love this toilet sink combo concept. What’s the best alternative without replacing my prized toilet?”

Heard of SinkPositive? It’s a fixture with a sink and faucet which takes the place of the toilet tank lid. You can retrofit your existing toilet with SinkPositive. Nothing will change except for the refilling part.

How It Works?

With a little tweak to the connection in the tank, water now takes a different route into the tank. Instead of the refill tube connected to the overflow tube or pipe in the tank, it is now connected to the sink faucet. The drain outlet of the sink is then connected to the overflow tube.

Now when you flush, the clean water will flow through the faucet for washing your hands. The used, or grey water then flows out through the sink drain and into the tank. Just like usual, the float ball in the tank stops the water flow once it rises to a level and shut off the fill valve.

So now with the sink on top of the toilet, the tank and bowl gets filled up as usual. The unusual part is, you get to wash your hands for ‘FREE’.

Here’s the video showing how easy it is to install a SinkPositive onto a regular toilet.

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When you broke your tank lid, don’t bother to get a replacement. Buy SinkPositive instead, you will love it.

Clean water is for drinking and cleaning our body, and grey water is for clearing waste. Makes perfect sense.

Why Should You Need A Toilet Sink Combo Unit?

You don’t need a reason to have one installed. But here’s some suggestions why a toilet and sink combination unit is right for you.

  • You want to separate the toilet from the bathroom, like the Japanese. Or you want to make use of a small space for a toilet, and that there’s no space for a sink, this will be a good solution.
  • You care about conserving water. And using all clean water for toilet flushing is, in your opinion, unconscionable. So you want to re-use the water you use to wash your hands for flushing the toilet. That makes you feel better than using 100% clean fresh water.
  • You want to improve toilet hygiene in your home, or maybe even your work place. By keeping the hand washing within the toilet area, you eliminate possible contamination.
  • You are a nice person and you want to play a part in conserving precious water.

SinkPositive – The Pros And Cons



  1. Quick and easy to install. Even without the manual, it’s easy to figure out what part connects with which part. So please don’t call the plumber.
  2. Touch free hand washing. No more turning of faucet knob or handle after the dirty paper work and risk contamination.
  3. Convenient and visual cue motivates hand washing. A survey has shown that 1 in 5 people don’t wash their hands after using the toilet. So when flushing, the sight and sound of water flowing from the faucet might encourage hand wash.
  4. Perfect solution for small spaces intended for a toilet and sink. And remember to install an exhaust fan or else the odor will have everyone avoid using the toilet.
  5. No sensors needed, so no need electricity for power and no worries of power failure.
  6. It does not change or affect the normal working of the flushing system and the usual way you flush the toilet.
  7. Clean water for your hands, grey water for flushing. In fact, the grey water with soap cleans the bowl better. You will find the bowl is cleaner and smell better compare to when you use only clean water to flush.
  8. Totally eliminates all possibilities of the tank water backflowing into the clean water supply. Though this backflow issue is rather remote with modern toilet design, still there is a risk with human error or a defective fill valve. Now with the total isolation between the tank and supply line, no chance a backflow will happen.
  9. Saves water and money. Now the water capacity provides for flushing, rinsing and hand washing.
  10. Made in the USA and fit snugly for most American toilets.


  1. Made of plastic. Some say it feels cheap compared to porcelain. Well, the idea here is for quick and easy installation. If you have ever assembled an Ikea chair or table before, this is even easier. The advantage of plastic is better elasticity. It won’t break if you drop it.
  2. Pricey for a plastic product. However, this is made in the USA. The manufacturer could have had it made in China or Mexico, but at the expense of job opportunity back home. So take it that you save water and the environment, and you help some folks provide food on the table for the family. And money stays in the country.
  3. Only available in White. If you want a sink which matches the color of your toilet other than white, sorry no go.

DIY-ing A Sink On Top Of Toilet Tank

As you can see the construction of the SinkPositive is very simple. You can diy a similar setup if plastic didn’t quite appeal to you.

A glass or porcelain bowl sink, a length of 1/4″ x 2′ copper tube and the necessary materials are all you need. The work quality is up to your diy skill.

The most challenging part is drilling a hole on the tank lid. You will need a porcelain drill bit set and a good power drill. Once you get pass this part of the entire set up, the rest is easy.

This setup is not suitable for dual flush toilets with the push-buttons on top of the tank cover. But that does not mean you can’t have a similar toilet sink combo that uses water from the tank.

Study how the water flows from the supply line into the tank and bowl, your creative mind is never short of a solution. Regardless of the toilet design.

But if you prefer an integrated solution, go with a Dual Flush Toilet Tank with Integrated hand washing basin like the Caroma Profile Smart.


  1. Hi there, apart from the Roca W+W, are you aware of any other sink/toilet combo that has inbuilt water filtration?

  2. Hi there, We are looking to buy a toilet and sink in one (like your top right picture) – do you know where I can get that? I saw one at a hotel in Miami and would like the same for my 3 new toilets in a remodel.

    • Hi Yuh.

      That’s a Caroma Profile Smart 305. I think the company no longer produce that model. You may want to check with

  3. WhrrW can I buy the ubitl that is curved with sink and toilet side by side? Thanks

    • Hi Jasmine. It’s by Roca. But not sure if it’s available in the States. You can check with them or do a Google search for “Roca W+W WC and basin”.

      The model is A893020001.

  4. Warm water will lead to increased formation of biofilms. Although I find this type of toilet extremely economical, hand washing with soap quickly leads to heavy deposits in the tank, which in turn leads to problems with the valve. It´s better, if possible, to use rainwater for the tank.

  5. really neat product, but I like using warm water to wash my hands. any way to incorporate hot water?

    • Hi Valinda.

      You can if you run a hot water piping to the supply line that feed the toilet tank. 🙂

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