How to Install a DIY Rainwater-Flushing Toilet System (Video)
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But this DIY rainwater flushing toilet from the UK is about as low-tech and effective as it gets. Using an upstairs balcony to house a barrel cistern; a simple gauze filter system; some charcoal for purification, and then some gravity-fed piping to a downstairs toilet cistern, the system automatically feeds the toilet cistern with rainwater whenever it's available. When rainwater runs out, the homeowners simply switch back to the mains water.