I am a student, and I am planning a solar water pumping system to supply non-potable water to a public bathroom on a Island. I am having a hard time finding a toilet to use in this system.
We are planning on having a large above ground storage tank to hold all the water. My biggest question is what type of toilet can be run on low pressure as the holding tank may only be 5-10 feet above the bathroom. We are trying not to have to install a separate pump to pressurize the system.
We are assuming a gravity feed toilet would be just fine, as most toilets are gravity feed. Most of the literature that I have read on gravity feed toilets suggest a water pressure of about 20PSI, which would require considerably more head.
It sounds like you need more consideration of other options. I can’t design a system on a free web site as we do not have the time and would never know all of the design parameters for the hundreds of request we get. However, I will give you some things to help you fine tune your design process.
1. You say you will have a large water storage tank, which in turn will provide water to flush toilets. It’s a law of nature that for every foot of height you raise any tank, the pressure at the bottom outlet will increase .43 psi per foot of height. You do not need to raise a large heavy tank, you could raise a smaller tank up on a nearby hill and fill it from the larger tank.
2. Consider waterless urinals and cut the total water usage by 50%. http://www.airdelights.com/waterfree_urinal.html
3. Use a second pump and pressure tank feed from the large storage tank. You can get any pressure and flow you want by selecting the right pump, which can be powered from a solar-charged battery. These require clear water entering so you will need some kind of filter between the tank and the pump.