Save (a Little) Water With a 3D Printed Toilet Sink!




About: Hi I'm Michael! I love all things Science, Engineering, & 3D Printing. If you've enjoyed my work then I've love to hear from you!

Not long ago I saw an instructable on hacking a toilet for free water and I wanted to see if I could make my own version using my 3D printer.

In summary, a 'toilet sink' is just a simple plumbing hack that lets you wash your hands with the fresh water a toilet uses to flush. In this way it can reduce your water consumption by eliminating the need to use even more water to wash your hands. The toilet sink also has the benefit of helping keep your toilet bowl clean!

This instructable will show you how to make a 3D printed toilet sink and make it waterproof, even if you did a horrible job printing it!

Step 1: How Much Water Does It Save?

To save myself a bunch of grief in the comments section I'll go ahead and immediately point out that there are much better methods of saving water than this. To quantify that, I did a little experiment to estimate how much water this thing can save.

I measured that I use about 4 cups of water to wash my hands in a normal sink. If I normally flush the toilet 5 times in a day every day for a year then I'll consume 456 gallons per year. Sounds like a lot but how much water is that is practical terms?

A typical American adult uses between 80-100 gallons of water per day. The average price of water in the United States is about $1.50 for 1,000 gallons, and you can expect to pay essentially the same amount for sewer costs. So that 456 gallons translates into a savings of $1.37 per year. (Californians can triple that.)

My toilet sink probably cost me about $20 in materials, so I'm looking at a 14.6 year payback period...

Clearly the primary benefits here are the novelty, the cleaner toilet bowl (from your hand soap), and knowing you've reduced your water consumption by some degree.

Step 2: Improvements to Original Design

Again you can see the original design here. Here are the primary things I've done to differentiate my design.

1. Obviously mine is 3D printed so the design is much more repeatable & easily shareable.

2. Instead of a plywood tank lid I used a shelf. The shelf was great because it looked better, it already the correct dimensions, and the outer surface is more water resistant.

3. Rather than dumping the used grey water into the tank I dumped it back into the overflow tube where it was intended to go. Dumping that water into the tank would likely leave behind a scum buildup over time.

Step 3: Parts List

(2) Printed Basin Halves

(1) Printed Faucet

(1) Board or a wall shelf that will fit your toilet tank

(1) Nylon Hose Barb 1/2" NPT and for 1/2" ID tube

(1) 3' of 1/4" ID vinyl tube

(1) 1' of 1/2" ID vinyl tube

(I've provided the model files in case you don't like my simple square design. The format is from Cubify Design.)

Step 4: Repair & Waterproof the 3D Printed Parts

Long story short my print settings were messed up so I ended up having major warping issues on the parts. (I didn't want to waste them after 8 hours of printing either.) That's OK though because you can easily repair parts using a thick slurry of ABS glue (Acetone + ABS scraps). Just spread it on with a putty knife and let it dry. The result will be a smooth waterproof surface.

Step 5: Glue the Parts Together

Use the ABS glue to bond everything together. Try to minimize the lumps at the seams because the paint wont hide them!

Step 6: Sand & Paint the Assembled Parts

Now that it is completely dry use a razor and sandpaper to scrape off the lumps as much as possible. Then I used a sandable filler primer to prime the plastic and to help fill up any small cracks. After that dries you have to sand it again and dust it off before painting it.

Step 7: Assemble Components

Cut the hose barb shorter so that it wont stick up inside the sink basin. Then screw it into the bottom of the printed basin and put hot glue around it to ensure that it is waterproof. After it cools you can attach the drain tube. The fresh water will come through the small hose which is run all the way through the faucet up to the top.

Step 8: Install

Connect the tubes as shown in the pictures. The fresh water comes from the pressurized refill tube. Just make sure you clean the connections really good.

The sink drain is pushed into the overflow pipe. When you flush the soapy sink water dumps directly into the rim of the toilet. You will notice that your toilet water becomes sudsy every time you flush. I'm counting on this to help keep my toilet bowls clean!

Step 9: Other Ways to Save Water

One of the major positives about the toilet sink design is that it doesn't require the user to change their lifestyle to save water. This is important because many of us won't take the environmentally friendly route unless its easy and doesn't require us to change our habits (i.e. there are many people who won't to let their lawn die to save water. For the record, I would).

Water is really cheap but that doesn't mean we should be wasteful! Here are a few water saving tips that don't involve major changes to your lifestyle.


1. Get a front-loading washing machine, which use ~60% less water than a top-loader (~30 gal/load saved) . (Front-loaders cost about $100 more than top-loaders, but common savings are $100/yr primarily from the reduced hot water consumption.)

2. Use a low-flow shower head (1.5 gal/min) rather than a standard one (2.5 gal/min) and save around 3,000 gallons per year per person (saves about $9/year in water and a lot more in heating energy).

3. Using a low flow toilet (1.28 gal/flush) instead of an older model (4 gal/flush) can save 10,000+ gallons per year per person (saves about $32/year).

4. Get a water conserving dishwasher, which use ~30% less water than a conventional one (~3 gal/ load saved)

5. Repair leaky faucets. (Unquantifiable savings)

6. Insulate your hot water pipes so you don't have to run the shower/sink as long to draw hot water. (Unquantifiable savings)

7. Buy a professional pre-made toilet sink, brand name 'sinkpositive'.


What are your favorite no-lifestyle-change water saving tips & tools? Let me know and a be sure to vote for this project in the Instructables Remix 2.0 Contest!

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    83 Discussions


    3 years ago

    why does she have a toilet? everybody knows that women don't use it lmao


    3 years ago on Introduction

    Saving $1.37 a year? Wouldn't buy a bottle of beer.

    "Grey water" reuse has been around a while as has the combined sink/WC, mainly to conserve space. Grey water gets properly stinky if left around for a few days and the whole idea of the flushing water closet was to do away with such nastiness.

    There might be some issues with potential cross-contamination of water supplies depending how you are plumbed.

    As a water engineer, I applaud anything that conserves highly purified drinking water, for many reasons. Who the hell needs to flush cr*p with drinking water?

    On the whole, people wash themselves and things far too much. 100-gallons a day? That's 33 builders buckets full or nearly 500-litres or half a tonne of water. I come from a generation when Sunday was washing night, Dad first, Mum next, me last, one tub.

    Here's my formula for water saving. Potable water for drinking and cooking only - that cuts water use to 20-litres or 4 gallons a day per person. Everything else uses rainwater, soft, free water, loads of benefits. Keep a compost heap. Pee is loaded with nitrogen, put it on the compost. Now for the really shocking bit. Use one of those builders buckets plus some sawdust for "solids". Get over the flushing thing, learn to love it. Centuries of societies have valued "black soil", midden pits, even the most advanced waste water (sewage) treatment plant recycle the solids as soil conditioners and treated liquids to return to streams and eventually drinking water.

    However - you might need a very understanding partner to share your habits.

    1 reply

    Reply 3 years ago

    Sharing habits with an understanding partner is not always your own thing and be and let live...freedom is more important than approval.


    Those who aren't interested in this for saving water could just put a decorative fountain there instead. Still the same concept, still pretty cool. If you were really in it for some serious water saving, you could convert your toilet to use collected rainwater to flush, instead of treated potable water. Anway, cool instructable!

    12 replies

    I did look it is NOT have the RIGHT to collect rainwater

    and don't let anyone tell you otherwise


    Reply 3 years ago

    People have been collecting and using rainwater for everything from gardening to washing their hair since long before you were born. Pretty sure it's not illegal anywhere, though the water sadly is not as clean and safe as it used to be.


    Reply 3 years ago

    In Colorado is not permitted "unless you own a specific type of exempt well permit", I remember some other states have similar laws, is not Federal.

    That's an urban legend that's been circulating. It's legal in all 50 states. Only Colorado has any restrictions.


    Well, my uncle Sam won't let me use his barrels to do it. He is using them for nefarious purposes.


    3 years ago on Introduction

    I'm not sure if it's an issue in practice, but this design could be considered a little unsanitary. Toilet bowls are glazed making it easier to clean and more difficult for bacteria colonies to take hold and grow. The inside of the most holding tanks I've seen is quite porous and could turn into a bacterial breeding ground for what is being washed off of your hands. I supposed one solution for this would be to have something like a chlorine or other chemical treatment in the tank itself, but it probably wouldn't work 100% and while you may be saving water you are adding more chemicals to the water supply which will take some amount of energy to remove down the line.

    3 replies

    You may have a valid concern. I know there is currently some nasty stuff living in my toilet tank (very old toilet, has not been properly maintained).

    However, if I am understanding this correctly, the water drains from the sink directly into the toilet bowl, bypassing the tank....

    "When you flush, the soapy sink water dumps directly into the rim of the toilet" (step 8)


    You're right I missed that. It looks like the drain from the sink is made to go right into the overflow tube and not into the tank itself, and as such it's not as much of a concern. So in that case, carry on!