Introduction: Toilet Top Sink

About: I'm an inventor / maker / designer based in the Bay Area. My background is in residential architecture, film set design, animatronics, media arts, exhibit design, and electronics. I use digital design and fabr…

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

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


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

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

  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

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

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

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.