About 20 years ago I put together a few rain barrels, eves troughs, some hose and a few fixtures so that my friend could flush his toilet at the house until his water was hooked up. This set up worked so well that he never took it down, but now he uses it to water his garden. Water spouted into the first barrel from the top floor eves, 2 barrels on an 8ft stand, inter-connected at the top so that most of the debris stayed in the first barrel. A tap was fitted 8 inches/ 20 cm from the bottom on both of the barrels (in case only one is filled, dry spell). The hose was fitted to the second barrel, when hooked up for the toilet a special fitting was made for connection to the toilet. It took longer to refill the tank but it worked.
"We 'Prep.' to live after a downfall, Not just to survive."
Really cool idea...must have saved a bundle these years flushing. We use grey water at times to flush, and usually only flush if needed. The only trouble is, if power is lost to the pump stations, you can flush for a while but the sewers will eventually back up.
We made a sawdust toilet, and have tried it out so we know it works. When we build in the country, this will be our only black-water plumbing. If you are interested, search for Humanure or Joseph Jenkins. Lots of vids out there and the book is available free in PDF with plans to make a simple system.
One day, the lowly farmer will be King