Toilet-Sink Combo: A Clever Use of Bathroom Space

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Have you ever seen a toilet-sink combo? We bet you haven’t because the thing is not exactly popular in the western world.

But if you want to remodel a bathroom or create a small toilet room, this may be the best option. So what is the toilet-sink combo? It’s a combination of the standard toilet and the sink with a faucet.

Perhaps it sounds unnecessary, but the combo has the purpose of saving space and water. And these aren’t the only benefits of the toilet-sink combo, so keep reading to learn how it works. 

How Does the Toilet-Sink Combo Work? 

To understand how the toilet-sink combo works, you need to know the mechanism behind standard flushing toilets

Traditional Toilets

Traditional toilets have a supply hose connecting the toilet to the main water supply line. Here’s how water gets to your toilet:

  • Clean water goes from the main supply line to the shutoff valve
  • The shutoff valve usually hangs on the wall behind your toilet
  • The valve transfers water through the metal hosepipe, leading it to the fill valve
  • The fill valve is at the bottom of the toilet tank, so it fills the plastic reservoir with water
  • When you flush the toilet, the water from the tank drops to the bowl to empty it
  • The toilet starts refilling automatically

What matters is that the water flowing into the toilet tank is always fresh. You’ll never reuse wastewater because it goes directly to the sewer.   

Toilet-Sink Combos

A toilet-sink combo follows a similar pattern, but it comes with a little tweak. Let’s take a closer look.

Clean water flows from the main supply line to the shutoff valve. After that, the water continues its journey from the shutoff valve to the fill valve — this part is the same for both toilet models. However, things take a different turn now:

  • Instead of filling the tank, clean water goes through the special tube from the fill valve to the sink faucet
  • The mechanism opens the sink faucet automatically when you flush the toilet, so you can wash your hands
  • Dirty grey water from the faucet flows into the toilet tank to fill it
  • Once full, the tank’s filling mechanism closes — it also stops the water from coming out of the faucet 

The water you use for washing your hands does not flush the toilet right away. Instead, it stays in the tank until you use the toilet some other time.

Benefits of Toilet-Sink Combos

A toilet-sink combo serves as a multifunctional unit. As such, it gives your household a number of practical benefits.

It Saves Water

The most important benefit of the toilet-sink combo is water preservation. Instead of using different water for flushing and washing hands, you can cut the consumption in half.

The same amount of water will serve both purposes — you can wash your hands and then utilize grey water to empty the toilet bowl. Most toilets consume 1.28 gallons per flush, but you don’t have to double the amount by using fresh water two times.

It makes a huge difference, particularly if you know that the average person flushes the toilet four times a day. With the sink-toilet combo, a single user saves nearly two thousand gallons of water annually.

The Combo Reduces Utility Bills

The second advantage goes hand in hand with the first one. When you reduce water consumption, utility bills shrink big time. It’s a major cost-saving feature that protects the family budget while helping the environment.

It Saves Space

A cute toilet-sink combo saves space in the bathroom. It’s a compact unit, so it takes no extra room to install it. 

The logic is clear — you must place a toilet in the bathroom, but you don’t need to use additional space for the sink.

Improves Hygiene

According to the report, over 40% of US adults don’t always wash their hands after using the toilet. It’s an awkward habit, but toilet-sink combos can help fend it off.

It’s easy to see why — the fixture practically forces users to wash their hands after flushing the toilet. The sink-toilet combo turns on the water automatically, reminding users that it’s necessary to wash their hands.  

It Cleans the Tank

If you use toilet tank cleaners to keep the toilet fresh and spotless, think twice. Strong chemicals may harm the toilet flapper and other fragile parts, while you also need to pay for the cleaning product.

On the other side, a toilet-sink combo does the same job without using additional cleaners. Hand-washing soap can keep the tank neat and clean, making your toilet smell nice around the clock.

The Same Flushing Efficiency

Some homeowners believe that the toilet-sink combo doesn’t have equal flushing potential as traditional toilets. This is far from the truth because the combo relies on the same flush system.

There are no differences between the two processes:

  • The flushing mechanism is the same
  • Both models use the same amount of water for flushing
  • The flushing power remains the same
  • toilet parts remain the same, including the toilet seat and the bowl 

Think about it for a moment, and you’ll realize it’s true. After all, the existing toilet remains the same — the tank, the bowl, everything. The only different thing is the tank top, but it doesn’t affect the flushing process.

Disadvantages of Toilet-Sink Combos

You’ve seen the pros of installing this toilet unit, but it’s fair to say that the fixture is not perfect. Like everything else, the toilet combo comes with a few downsides.

Not Readymade Available

The toilet-sink combos are not a mainstream product, so most manufacturers produce them in small quantities. It may take a while to get your combo in stock, especially if you need a toilet unit that fits a certain bathroom size or shape.

Low Accessibility

The main disadvantage of the toilet-sink combo is low accessibility. A typical person can approach the sink with ease, but that’s not the case with specific user groups.

For instance, the kids and the elderly will have a hard time accessing the toilet-sink combo due to its unusual position. The same goes for persons with disabilities, especially the ones in wheelchairs.

Keep in mind that many toilets occupy bathroom corners, while the bowl covers the front of the sink. This means that the only way to approach the toilet-sink combo is on the side — a slightly uncomfortable position for some users.

Cold Water Washing

If you love washing your hands with warm water, we have an unpleasant surprise for you. The toilet-sink combo has only a cold water supply, preventing you from washing hands with warm water.

Most people don’t make a big deal of it, but we just want to remind you of this little detail.

Toilet-Sink Combo: Water Flow Rate

Another thing we need to discuss is the washing efficiency of the toilet-sink combo. One of the most common questions we hear from our readers is: “Does a toilet-sink combo have a fast or slow water flow rate?”

It often seems like the water is merely leaking out of the faucet, so it’s natural to ask this question. However, the water flow rate does not depend on the toilet combo itself. On the contrary, it depends on water pressure coming from the supply line.

How come?

The shutoff valve behind your toilet controls the water pressure. If you don’t open it to the fullest extent, the pressure is lower, and the faucet delivers a weaker stream of water. But if you open it fully, rest assured the pressure will increase.

Here’s how you can open the shutoff valve to the fullest:

  • Identify the shutoff valve — it’s a small knob behind the toilet
  • Grab the knob with your fingers and twist it counterclockwise
  • When the valve goes a full circle, it is open

Sometimes the shutoff valve won’t shut off because it’s stiff and rusty. In this case, use penetrating oil like WD-40 to spray the knob. Leave it for 10 minutes — the oil will do its thing and loosen the valve. After that, twisting the shutoff valve will be easy.

Popular Combo Toilet-Sink Options

Now you know how toilet-sink combos work, so the only thing left is to show you a couple of popular models. 

Sink Again 

Toilet-Sink Combo: A Clever Use of Bathroom Space 1Toilet-Sink Combo: A Clever Use of Bathroom Space 2

Sink Again is a widespread solution among combo toilet-sink lovers. It has a curvy sink that fits into the tank seamlessly. The installation process is simple and effortless, taking only a couple of minutes. 

You can install this unit in the bathroom, toilet room, or powder room. It’s a white combo unit, which means you can install it in most toilets regardless of the design.

Sink Twice for Large Tanks

Toilet-Sink Combo: A Clever Use of Bathroom Space 3Toilet-Sink Combo: A Clever Use of Bathroom Space 4

Sink Twice for large tanks is another combo toilet sink that saves water, money, and space. It enables touchless hand washing, taking the hygiene level to the maximum. 

The best thing about this sink combo toilet is that it suits different toilet tanks. You can put it on larger models without worrying about the stability of this sink combination unit. 

How to Install a Toilet-Sink Combo?

Adding a toilet-sink combo to the existing toilet requires minimal plumbing knowledge. Anyone can do it – the only thing that matters is to connect a couple of plastic tubes. Here’s a step-by-step manual on how to do it.

Step 1: Purchase a Toilet-Sink Combo

The first task is buying a toilet-sink combo. If you have a small bathroom, the best option is to get a tiny sink that doesn’t occupy too much space. However, you also need to check whether it suits your toilet tank.

Our advice is to go for Sink Twice as it’s a lightweight but durable model. You can install it with ease, especially if you follow the PDF product manual. Sink Twice is a white-colored plastic sink, which means it perfectly fits your white toilet.

Step 2: Remove the Tank Lid

Now that you have a new toilet-sink combo, it’s time to install it. Your first job is removing the tank lid. The task requires minimal force — you will grab and squeeze the sides of the tank, lifting it from underneath.

If you can’t do it, use a flathead screwdriver. Insert its sharp tip into the hairline crack between the tank and the top. Push the lid upwards, and it will snap off almost instantly.

Step 3: Connect Your Toilet-Sink Combo

The tank is now open, so you can identify the fill valve and the overflow tube. The fill valve is the highest plastic tube in the tank, and you can find it on the left side. The overflow pipe is on the right – this part is a couple of inches lower.

You’ll notice that the toilet-sink combo also has a couple of plastic tubes under the faucet. Your job is to attach the two tubes to the fill valve and the overflow tube.

The one that attaches to the fill tube’s nozzle is usually clear and transparent — this tube delivers clean water to the faucet. The second tube (AKA discharge tube) is often black, and it transfers dirty water from the sink to the overflow pipe. 

From there, grey water exits the tank and goes to the toilet bowl.

Step 4: Connect the Sink to the Tank

After connecting both tubes, you can finally set up the sink. Doing it is easy as you only need to snap it onto the tank’s rim. Plastic parts fit together well, so it doesn’t take much force to install the toilet-sink combo.

The Bottom Line

The toilet-sink combo is not the most popular bathroom unit in the western world, but there’s no reason to avoid it. On the contrary, the toilet-sink combo gives your home many useful benefits.

It makes the toilet clean, saves water and your budget.

You can install the toilet-sink combo in minutes. All it takes is to connect two pipes with nozzles inside the toilet tank. After that, your toilet-sink combo will operate effortlessly.

Do you have more questions about the toilet-sink combo? Make sure to leave a comment — we’ll be glad to answer!


What is the combination toilet?

The combination toilet is the fixture containing both the toilet and the sink with a faucet. In this case, the basin and the toilet have different water inlets — the combination toilet uses cistern flushing.

Modern combination toilets provide users with extra features such as the toilet paper compartment and towel rack.

Why do Japanese toilets have sinks?

The toilet-sink combination is popular in Japan because the country lacks residential space. Japanese manufacturers produce many combos to help people fit the existing toilet into small bathrooms. 

It’s a matter of culture and space preservation.

On the other side, manufacturers in western world countries rarely make the toilet-sink combo. They count on a different plumbing code that doesn’t promote the use of this toilet unit.

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