My previous post described how I collect rainwater into a small raised tank at the end of my garden. The aim was to be able to use this water to flush the toilet.
The next step was to figure out how to get that water into the cistern, without disrupting the existing plumbing. I wanted to be sure it could still flush, even if the rain water tank was empty, or something else went wrong.
I live in an old house, and the cisterns were fitted with overflow pipes which led outside. Since the new flush mechanisms overflow directly into the toilet, this overflow pipe was unused. So I could run a pipe from the tank to this overflow pipe where it protruded through the outside wall of the bathroom.
That would allow water to run from the tank into the cistern, but there would be nothing to stop it overflowing. Some mechanism was needed to stop the flow when the cistern was full.
The standard mechanism for refilling is a float valve. It is designed to work from high pressure (municipal water), so if I connected that to my very low pressure gravity fed system, it would not work. The water pressure would not be enough to open the valve fully.
I asked around some local shops for a low pressure float valve, but didn’t find anything. It was time to start designing…
I decided to use ABS plastic, as it can be well sealed using acetone vapour. All that was needed was a block which could be attached to the old overflow pipe inside the cistern, which could be closed off by a hinged plate which could be lifted by some sort of float. The actual valve could be silicone rubber which I would smear on afterwards and allow to set into the exact shape of the plastic. A ridge or two would help create a seal, and rows of small holes in the plate would allow the silicone to bond firmly onto it.
I tried to design an arm which could hold two table tennis balls as floats. It didn’t seem to have the lift needed to seal the valve, so instead I cut off the aluminium rod and float of a standard ball valve, and pushed that into the plate I had printed. In addition to being simple and cheap, this allowed some adjustment by bending the aluminium rod.
To get the water to the overflow outlet on the outside of the wall, I ran some irrigation pipe from there to the tank. At the tank side, I installed a non return valve just after the tap, so that water could flow to the toilet, but never back into the system, even if the pump was sucking water from the tank.
In the end, it turned out to be easier than I thought. It has been in place for months now, and has worked perfectly. If a flush uses 6 litres of water, the 260 litre tank will give about 40 flushes. I have a ‘hold open’ multi-flush system installed, so if that uses 3 litres per flush I would get about 80 flushes after a good rain.
That was all good and well, but what about those times it didn’t rain? The obvious next step was to add some DIY well points to extract water from the ground. How hard could it be … ?
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