Introduction: Toilet Top Sink

Picture of Toilet Top Sink

A single toilet flush uses about 3 gallons (13.5 Liters) of potable water. This project re-routs the fresh water that fills the toilet tank through a hand washing sink, filling the tank with grey water for the next flush and saving the water you would have used to wash your hands separately.

Why use water you could drink to flush a toilet? This is a huge waste of a precious resource, especially in the epic drought we're experiencing in California. This project is a way to save water in style, using a plastic coated Plyboo sink and sleek faucet by Moen.

Step 1: Design

Picture of Design

This idea has been in use in Japan for at least 30 years, but I wanted to design something more elegant than the one's I've seen commercially available. There are a lot of materials you could use to to make this project. I was thinking of cast concrete in the beginning because it's a moldable material and can be made waterproof with the right sealant. I finally decided on a wooden box with a sloped basin because I love the aesthetic. Wood is usually associated with rot when combined with water, but with the right materials and maintenance it can last just as long as concrete.

The first step in designing anything is measuring. First, I made a template of my toilet tank by placing a piece of stiff paper on top of the open tank, and tracing around it with a felt pen. It wasn't very precise, but it was close enough for me to plan for the appropriate size for the sink box.

With a scanned template to work off of, I designed the box in Fusion 360 (it's free with an "enthusiast" license, and it does everything I need it to). Moen has 3D models available for download for a lot of its projects, so it was easy to insert the model of the 90 Degree High Arc Vessel Bathroom Faucet and design around that. Having the model of the faucet made it easy to work out dimensions and proportions, as well as aesthetics that work with all the components.

With the model completed, I was able to quickly make templates for use with the router so I could quickly and precisely fabricate the piece.

Step 2: Tools & Materials

Picture of Tools & Materials


90 Degree One-Handle High Arc Vessel Bathroom Faucet by Moen- This faucet is a gorgeous piece of industrial design- the clean lines and right angles fit perfectly with the design of the wooden box.


  1. Plunge Router
  2. Clamps + Wood Glue
  3. Screw Gun
  4. Channel Lock Pliers, Crescent Wrench


  1. Plyboo sheet (about 2' X 3' total for the project)- You could use just about any kind of wood as long as you apply the polymer coating for waterproofing. The material will have to be exactly .75" thick for it to work with the templates I've provided.
  2. Ultra-Glo polymer coating- This is an easy to use 2-part pour-on plastic finish. I like it because it's pretty benign in terms of toxic chemicals (no nasty fumes to speak of), and it mixes in equal parts, which is much easier that measuring something like epoxy.
  3. E-6000- This is a super versatile multi-purpose construction adhesive. It bonds to metal, plastic, wood, glass, etc. and it's waterproof. This comes in handy when creating a waterproof seal around the drain strainer.
  4. Teflon Tape- This is used to create a seal between the threads of plumbing parts and prevent leakage.
  5. 1/2" ID Clear Vinyl Tubing- This is used to connect the toilet fill valve to the faucet.
  6. 3/8" Brass Compression Tee- This connects the clear vinyl tubing to the two (hot and cold) water hoses on the faucet.
  7. 3 in Strainer Drain- This connects to the drain hole in the bottom of the sink basin, straining out hair and other large particles, and creating a watertight seal that protects the bottom of the basin from water damage. Water from hand washing drains directly into the tank from this drain.

Step 3: Cutting Panels With Templates

Picture of Cutting Panels With Templates

With a little patience and a lot of practice, this whole project could be done with a Japanese flush saw and some chisels. I used a router and templates to save time.

  1. Create the templates
    • I had these templates laser-cut because it's a fast, accurate way to accomplish this step. There are services everywhere that do this for affordable prices. Ponoko is a good nationwide service for laser cutting, and since this is a small job it won't cost an arm and a leg.
    • If you want to save money, it's totally reasonable to create these templates with a bandsaw or jigsaw and a chisel. Check out my Digital Fabrication by Hand instructable for more info on how to do that.
    • I used 1/4" masonite for the templates because it cuts easily and is the right thickness for the router template guide.
  2. Apply the templates
    • Another big bonus with laser cut templates is that the parts interlock perfectly like a puzzle. To apply the template. The templates all have three parts: (1) A perimeter piece that's offset 3/4" from the edge of the part template, (2) the part template, and (3) the offset piece between the two.
    • Since they're laser cut, I just placed the entire piece on top of the wood, drilled countersink holes in the template, screwed it down with countersunk 1/2" screws, and removed the offset piece with a putty knife. The perimeter piece gives the router base a surface to bear on- this keeps it flush.
  3. Set up the router
    • I used a plunge router because it makes a repetitive job like this much faster. It's not advisable to rout out a piece of wood in one pass- you could break the endmill or start a fire- so you have to do it in steps. I've found 1/4" at a time is pretty comfortable. The plunge router I used has an adjustable stop with a pin which allows you to set the step on the fly. I cut these pieces in 3 steps, starting with 1/4" deep, then 1/2" deep, then 3/4" deep.
    • I chose a 1/4" 2 flute endmill for this cut. The template guide that fits a 1/4"Ø endmill is about 9/32"Ø on the outside, and this is the part that bears against the edge of the template. It's important to keep this in mind because the finger joints will end up being 1/16" smaller (on the inside) and larger (on the outside). This can be fixed by filing the joints, or preferably by offsetting the template lines to account for the diameter of the template guide. I didn't do this for the template PDF files I've provided here, so if you want to use the same ones you'll have to make the measurements yourself according to the diameter of your template guide.
  4. Rout out the pieces
    • This is the time-consuming part. Between each 1/4" increment, I stopped the router, picked out the packed sawdust with a screwdriver and vacuumed it up. You may not need to do this with other materials, but plyboo creates nasty, dense, sticky sawdust. If you don't vacuum it out, it's very easy to start a fire!
    • I repeated this step with each of the 5 finger-jointed pieces of the box.
  5. Sloped panel for sink basin
    • The sink basin has a sloped panel the meets at a mitered edge at the top and bottom. The top miter is 48º and the bottom one is 42º. You could certainly make it with two 45's, but I didn't like the proportions of that, so I went wit these weird measurements.

Step 4: Prepping and Joining the Panels

Picture of Prepping and Joining the Panels
  1. Square finger joint edges
    • Using a router to cut the finger joints has a downside: the inside corners have a radius because the router bit is round. To square up these corners, I used a corner chisel.
    • This can be difficult to keep square to the inside of the cut sometimes, so I also tried this on the band saw, which worked just fine as well.
  2. Glue and join
    • This step is pretty straightforward. I made sure there was glue spread on every surface of every finger joint that touches another surface, and clamped the whole piece together. I used a paintbrush and some water to clean up the excess glue and avoid scraping it off once it's cured.
    • I hadn't tightened my router bit enough, and the bit drifted down on one of my passes, leaving a nasty groove in the plyboo. Thankfully I was able to hide this mistake on the underside of the box. I used Bondo to fill in the gap.
    • A bunch of trigger clamps did the trick of keeping the piece in place while the glue cured overnight.
  3. Check and prep for waterproofing
    • I inserted the strainer drain to make sure it would fit (should have done that right after I drilled the hole!).
    • With the dimensions verified and the gash patched up, I sanded the whole piece with 120 grit sandpaper using an orbital sander and did a quick swipe on each edge with a sanding block to take care of any splinters leftover.

Step 5: Waterproofing

Picture of Waterproofing

For waterproofing, I used Ultra-Glo polymer coating. It's very easy to mix- adding equal parts from both the A and B bottles, I mixed it vigorously with a stirring stick for 2 minutes.

After 2 minutes of stirring, I poured the coating liberally on a test piece and spread it out with a putty knife. After about 6 hours, the piece was totally cured and completely waterproof (at least where the plastic was).

There were some tiny bubbles left in the surface. The instructions say that you can mitigate this by blowing on the curing surface or using a propane torch. It isn't heat that breaks the bubbles, it's CO2.

Feeling comfortable with the process, I mixed another batch of Ultra-Glo and spread it onto the finished box. I did my best to burst any large bubbles and spread an even coat on the whole piece. This is difficult because the material is pretty viscous and wants to run down the sides in streaks, but spreading over the surface with a spatula for about 5 minutes got everything fairly even.

Step 6: Attaching the Faucet and Pluming

Picture of Attaching the Faucet and Pluming

Attaching the faucet and hooking it to the plumbing inside the toilet tank is really simple. Here are the steps:

  1. Apply some E-6000 to the rubber gasket on the drainer strain, then insert it into the drain hole and tighten the nut with some channel lock pliers.
  2. Assemble the faucet using the manufacturer's instructions. All you have to do for this part is add the vessel extension and the trim to the underside of the faucet, insert it into the hole in the box, and add the washer and nut and tighten it with the too provided.
  3. The two faucet hoses attach to two of the outlets on the tee fitting- these are intended for hot and cold water, but in this case we only have cold water. It makes sense to attach both of the hoses to a tee instead of capping one and hooking up the other, because with both the hot and cold hoses attached there's no need to pay attention to which way the valve is turned when the toilet is flushed. The faucet will output an even mixture from both tubes no matter which way it's turned. Remember to use Teflon tape on the tee fitting ends!
  4. The third outlet on the tee fitting attaches to the vinyl tube using a barb fitting (included with the tee).
  5. There will already be a tube attached to the water spraying outlet on the toilet valve (if your toilet is like mine). This must be removed, and the vinyl tube attaches to the male barb end on the water spraying valve.
  6. The water hoses must be carefully placed inside the toilet tank so that they don't get in the way of the lever or the flapper.
  7. I added some 1/4" dowels to the inside corners of the bottom of the box to keep it in place on top of the tank. These will vary in location depending on the exact measurements of the toilet tank it's intended to be placed on. This feature could also be executed with stainless steel screws.

Step 7: Save Water in Style

Picture of Save Water in Style

The sink is really simple to use. Before flushing, just make sure the valve is open, and watch the water pour out. You'll have plenty of time to wash your hands as it usually takes about half a minute to refill the tank.


natalia2 (author)2017-05-21

Hey! Couldn't find your website. I'm interested in finding out how much it would cost us for you to make our sink. :) How can I get in touch with you?

JON-A-TRON (author)natalia22017-05-22

Sorry, that's an old link above. Here's my current site:

rskyme (author)2017-04-05

I love this idea, and from what I have read the sink positive is made from plastic and is not attractive,much prefer this!

bobsacomano (author)2015-11-21

I love this, but that faucet is $800 MSRP! I'll need to find something else in my price range.

CulverV (author)bobsacomano2016-10-17 has two "toilet sinks" (Sink Twice and Sink Positive).

JON-A-TRON (author)CulverV2017-01-19

Yeah, but then you don't get to make anything.

JON-A-TRON (author)bobsacomano2017-01-19

You could also just use a gooseneck spout- Not as pretty as the Moen, but it works just as well.

with savings on water I am sure you will get that back in no time. lol

nhbench (author)2016-03-23

Awesome! My wife and I just visited Japan and have been raving about the advantages of separating the toilet room from the shower room. We've also been going crazy wanting to find an over the toilet bowl for this very purpose! Great job! Thanks for your 'ible!

CulverV (author)nhbench2016-10-17

They are available on Amazon (toilet sink) or . I agree that the Japanese have led the way on this

JON-A-TRON (author)nhbench2016-03-24

Thanks! The Japanese do so many things right.

divasunny (author)2016-03-22

Where can I buy it ??

CulverV (author)divasunny2016-10-17

They are available on (toilet sink)

SherryR2 (author)2015-12-19

This is in no way sanitary, you need to wash your hands in the hottest water you can.If the water was hot, maybe it would be worth it.

FuzzyBearGeek (author)SherryR22016-07-04

Vigorous hand washing with soap is the most important thing. That whole HOT WATER thing just doesn't, well, hold water. Hahaha. ;-)

JON-A-TRON (author)SherryR22015-12-19

There was actually a long discussion about this on the Facebook thread. Apparently the heat of the water doesn't really make a difference in killing bacteria. All you really need is soap and potable water:

BobH77 (author)2016-03-16

How about draining from the existing sink into a side-mounted supplemental cistern. A valve prevents adding more to the supplemental when it is full.

A Siphon tube draws water from the supplemental cistern into the commode cistern as it is drained into the bowl.

Pro: nobody has to "Lean Forward" over the commode and cistern top to wash.

water and wash basin is not duplicated.

water diverted from wash basin drainpipe to supplemental cistern

siphon feed allows supplemental basin placement and design to expand re-used water volume.

this idea can be integrated into a manufactured commode with two cisterns with a communicating siphon feed.

Cons: siphon design is critical

JON-A-TRON (author)BobH772016-03-16

This method is definitely ideal, but there's no way I could convince my landlord to let me do that. Maybe one day I'll live someplace where I can afford to buy a house!

BobH77 (author)JON-A-TRON2016-03-17

found this comment below:

"Put hair and soap through a valve, and that valve will fail rapidly."

That gives me pause... add to Cons.

JON-A-TRON (author)BobH772016-03-17

How much hair do you think is going to get in there? It's only being used to wash hands after using the toilet. As for soap, I can't speak to that but this has been installed in my house for a year and the valve seems fine.

BobH77 (author)JON-A-TRON2016-03-17

For this design you presented, I think it would be rare to get hair in it....too uncomfortable to bend over it to shave or wash not much.

For what I suggested, to draw water off the existing basin, it is an issue as hair is known sometimes to clog the traps/pipes under wash basins. Any such design would have to be resistant to clogging due to hair picked up in grey water from normal wash basin. That's why it is a "Con" for what I suggested.

jdavis8 (author)2016-03-10

That's pretty sweet! Good job!

bliob made it! (author)2016-02-29

Very good job, but if you are a handyman there is an other solution :

CraftAndu (author)2016-01-20

A superb way to save water. Thank you for sharing!

mw6 (author)2015-12-04

this idea is brilliant!

tallemertes (author)2015-11-10

I love this idea. What happens if someone doesn't use the sink enough to completely fill the toilet bowl?

jcortez6 (author)tallemertes2015-11-20

It the water that fills your toilet that your washing your hands with

JON-A-TRON (author)tallemertes2015-11-10

That doesn't matter. The valve stays open, so all the water that would otherwise go into the tank just goes through the faucet first. Does that make sense?

BrianU2 (author)JON-A-TRON2015-11-12

I still don't quite get it... Normally the tank fills up after the last flush so that you can get a quick dump of all of the water in the tank to flush the bowl. I think some toilets (like those in public bathrooms) have a high enough pressure than the water can just come right from the pipe. If the water comes through the faucet first, I would imagine that the water that has gone into the tank so far would get quickly flushed, and then water from the faucet would take some time to work it's way down the sink and into the tank, having a second stream of water. It doesn't seem like it would provide enough force...

Also, maybe this is a rare case, but what if you go a while without using that particular toilet, but you still wash your hands in the sink? Is there something to keep the toilet from overflowing? Is there a way to tell how much water is in the toilet?

I also wonder about how comfortable it would be to stand astride the toilet to wash your hands. Perhaps it would make sense to reflow the pipe from an adjacent sink (I see one to the left of your toilet in the video)?

That said I think that this is a great idea. It just seems like a hacker's solution right now. It would be great if there was something with the kinks worked out that could be used by anybody without having to think about it. That's building something like that is, I think, how you can change the world at scale.

skylane (author)BrianU22015-11-12

the float valve in the tank shuts the water off when the tank is full

JON-A-TRON (author)BrianU22015-11-12

ptobrn has it right. I made this diagram, it might help explain what's going on.

IvanW (author)BrianU22015-11-12

They do have the kinks worked out, and production on a large scale. SinkPositive is just one of the companies that makes these. The reason I've been interested (But not yet willing to pay $130 or so) is that I have a toilet tucked under the stairs in my basement, with no room for a sink. That was well within code 65 years ago, but it is annoying.

ptrobrn (author)BrianU22015-11-12

the tank fill dumps water into two places. The tank which is the reservoir for the water that actually flushes and pushes the waste out of the bowl and down the pipe. The other is the small plastic tube that is the bowl fill and goes to the stand pipe. The stand pipe has two functions. It prevents the tank from over flowing onto your bathroom floor and allows the bowl fill to let water directly to the bowl so that it will fill with water. If your bowl didn't have water in it your waste would stick to the bowl and you don't want that... you want it to hit water first and it is less likely to stick to the bowl.

So what he is doing here is stealing the water from the bowl fill to wash your hands with and then dumping that water into the stand pipe. You do want to make sure that your drain is smaller than the stand pipe so that if your fill valve doesn't shut down the extra water will go into the stand pipe and not onto your floor.

vincent7520 (author)2015-11-13

nice, but I'd like to know why American toilets are not equipped with adual flush system that is so common in Europe : low flush and high flush ?

I just came back from a 2 months trip in USA and I never saw such a simple system in either homes and other private places or public.

Don't misjudge me : using grey water is even more efficient, but more complex to set up.

Thumbs up, anyway !

JeffreyA17 (author)vincent75202015-11-16

idk if it is in retail stores, but I know that my parents got that in their bathroom. Really, it's standard in Europe? i didn't know that. my parents may have bought it on their trip to Hong Kong or just ordered in from eBay. but it is possible for use to get it. but it is not standard or publicly known.

AndyL25 (author)vincent75202015-11-14

You may have noticed that we're pitifully behind Europe in ALL forms of conservation. Dual flush toilet are, at long last, appearing here. The Kroger chain of supermarkets, prodded by the Fred Meyer chain that they bought (West Coast, always ahead in sane living) is converting.

MinnyGufty (author)2015-11-14

Easier & cheaper to just lift lid off cistern & wash hands in the water, also providing grey water for next flush.

ZombieWorkshop (author)2015-11-13

Very cool it looks great in bamboo i will try to do something like this but in ceramic to match the toilet syle

theNightwalker247 (author)2015-11-13

Really nice Projekt have to do it one day in a little downgraded way

mjd (author)2015-11-13

This is one of the things the Japanese have absolutely right. The homes I stayed in over there a few years back also generally had a little water activated air freshener in the sink on the tank to freshen the air.

By the way, an overlooked advantage of this is that you don't just fill the tank with gray water - it's soapy gray water and that helps keep the toilet clean.

RigelBlue (author)2015-11-12

I was in Japan about 10 years ago, and many homes had toilets with these attached. We just washed our hands with the water as it filled up the tank- as "hackerboysf" stated. The faucet was just a pretty chrome tube, over a ceramic bowl- simple.

Kaljakaaleppi (author)RigelBlue2015-11-13

Japan and other South-East Asian countries. In places where water is scarce (islands, anyone?) this is common...

swgrmn (author)2015-11-10

$800 faucet?? It would need to save me over a years worth of water before BE on just that single piece

neffk (author)swgrmn2015-11-11

Not everything is a business plan. Gotta compare costs to the right thing. If everything was about efficiency, the world would be a different place. It's not hard to spend 50 $ when I take my family of 5 out for dinner, for example.

The attitude of using less than you can afford is the key to ethical living, IMHO.

Also, you could do it for less, if you wanted. Or more!

AmyCat59 (author)neffk2015-11-12

I think the design's very nice... but it'd cost me 10x more for all the materials and tools than if I just spent $130 for a SinkPositive (even if I also paid a plumber to install it). Gonna bookmark this one, though, with the thought that the $800 faucet can be replaced with something MUCH cheaper (either a secondhand faucet from a reuse store, or, as another commenter says above, a nice piece of copper pipe since you aren't turning it on and off with the faucet-controls anyway). If I make one myself, I think I'd hand-build a ceramic basin and attach it to a well-waterproofed PlyBoo base. That way, I could build in a soap-dish on the side of the sink, too...

JON-A-TRON (author)swgrmn2015-11-10

Believe it or not, that's about mid-range for luxury plumbing fixtures.

DanT4 (author)2015-11-12

Grease from my hands goes into my toilet! What a great idea!

manskybook (author)DanT42015-11-12

Well, no, first the grease goes on your butt or wherever, and then you have 25 seconds to wash your greasy hands. Or you could continue to flush your toilet in order to wash your greasy hands. Maybe you should wash your hands somewhere else after you work on your car, and before your flush?

stratigary (author)DanT42015-11-12

This is for washing your hands after using the bathroom, not after working on your car. Regardless, if your toilet can handle the fats and oils in your fecal matter, it can handle a little of that off of your hands.

iamuke (author)2015-11-12

Appealing idea but you should never store greywater. All manner of goopy crud will accumulate and pretty soon you have a superfund site in your bathroom.

A better way to do it is a toilet that is designed to use greywater or blackwater from the get-go. Something like what Ken Kern designed in his book "The Owner Built Home".

About This Instructable




Bio: I'm a full-time Designer at the Instructables Design Studio (best job ever). My background is in residential architecture, film set design, film animatronics, media ... More »
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