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Build This Water-Saving Toilet Tank Sink


Jon-A-Tron from Instructables has posted a project on how to build a toilet tank sink. I’ve been thinking about adding one of these to my bathroom and this certainly makes DIY look very doable.

Jon writes about the project:

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 a sleek faucet by Moen.


A single toilet flush uses about 3 gallons (13.5 Liters) of potable water. A toilet tank sink works by routing the water that would normal go into the tank, which is clean water from the supply, through the sink on top of the tank. From the there, the resulting graywater goes into the tank and then into the ball for flushing.


The only peculiarity of this type of sink is that you have to turn the faucet on while flushing to refill the tank. That, and of course, washing your hands on the toilet. But hey, get over that. This is a foolish waste of water. Why not make it do double duty?


To create his sink, Jon-A-Tron used Plyboo (plywood made from bamboo) for the wooden tank, Ultra-Glo polymer coating for waterproofing, and a very fancy, expensive Moen faucet. This Instructable was sponsored by the well-known bathroom fixture company, hence the $600 faucet. If you’re going to build this, you could obviously use a much cheaper fixture.


Here’s a video of Jon-A-Tron briefly describing the build and showing how the faucet operates:


You can see the full project and find templates for this build on the project’s Instructable page.

This project is from a series on Instructables sponsored by the plumbing equipment company Moen. You can view all of the projects in the series on the Moen landing page on Instructables.

19 thoughts on “Build This Water-Saving Toilet Tank Sink

  1. Beautiful build but I don’t think the toilet tank sink is a great idea unless you live in the middle of the desert and water is really really precious.

    The thing is that all that soap, dirt and bacteria isn’t going directly down the drain. It will sit and fester inside the tank until it gets flushed. Then when it does get flushed, even if you held down the handle until no more water was flowing there is going to be maybe a cm or so of water that just sits in the bottom. That means that while you may eliminate the majority of the scum upon flushing there is always going to be a sample of very type of bacteria that ever got washed in ready to repopulate the new water.

    If you went away or something (or just used your other bathroom) and so didn’t flush for a while it could get pretty rancid. Also.. keep in mind, all those toilet parts, inside the tank, they do not last forever. They are meant to be replaced.. usually by the owner. Some day you will have to stick your hands down in that thing!

    1. agreed. And good luck keeping that bamboo sink clean over time. There’s a reason EVERY normal sink has rounded corners and no seams.

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    2. Also, I’d be worried that hand soap might play hell with all the rubber parts in the tank. Even chlorine in the water eats them up over time.

    3. You make some good points, but if the sink is situated properly, the sink drains into the overflow tube and into the bowl of the toilet, not the tank.
      In a toilet valve, there are 2 exits for the water. The first is at the bottom near where the valve penetrates the toilet tank, and the second is near the top of the valve, which is normally routed into the overflow via a hose.
      When you flush, the bottom outlet fills the tank, and the top refills the bowl of the toilet and ensures that the trap is filled with water.
      In this design, it appears that the sink is only being used to refill the bowl and trap of the toilet, not the tank of the toilet.

  2. There’s nothing “Foolish” about proper sanitation. Certainly it’s laudable to come up with clever methods of using waste water, but I live in a high rise where I’m lucky if TWO flushes will actually clear all the waste from my toilet. This setup looks to be a MASSIVE waste of time.

  3. Since ’94 water closets only use 1.6 gallons per flush. If you’re still using 3 gallons per flush the best way to save some valuable water resources is to buy a new fixture to replace your 20+ year old toilet.

    1. I have to flush those newer toilets 2 or 3 times after I take a dump. With the old style, only one flush was needed.

  4. This is one of those “projects” where money is not the issue but rather a display of fanatical eco-centric posing. There is no real water savings here and it is neither a practical nor hygienic way to wash your hands. It was originally posted in Instructables and being a “sponsored” article, they remove any and all comments that don’t support this ridiculous idea.

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  5. This is pretty standard practice in Japan for most toilets. They almost all have little sinks on top. You don’t use soap with the sinks. The toilet doesn’t run long enough after a flush to allow you to completely lather up and rinse off all the soap. The point is that you can give a little rinse after urinating. You still have normal sinks with soap for washing up after a big job. It’s an extra little step to help keep the inside of your bathroom a little more sanitary. Instead of grabbing the faucet handles with possibly pee splattered hands (you know good and well you don’t wash the faucet handles while washing your hands) and then grabbing them again after having JUST cleaned them, you can grab them with mostly clean hands and everyone is a winner. If you haven’t used one of these toilet top sinks, don’t be so quick to poo-poo on the idea. It’s definitely better than the current system you employ.

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Gareth Branwyn is a freelance writer and the former Editorial Director of Maker Media. He is the author or editor of over a dozen books on technology, DIY, and geek culture. He is currently a contributor to Boing Boing, Wink Books, and Wink Fun. And he has a new best-of writing collection and “lazy man’s memoir,” called Borg Like Me.

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