When we lost city water a few years ago (due to flooding) my wife and I started by collecting rainwater from our downspouts in small plastic containers and quickly repurposed some large rubber maid storage containers as makeshift rain barrels. Worked OK but with 6 downspouts and 2 people we were quite busy while it rained and "lost" more water than we collected.
The next day I went to the local hardware store and bought some PVC discharge hose, 1.5"ID and very flexible, and rigged it up to the sump pump discharge with some duct tape and an 18 gallon rubber maid container as a "rain barrel". Worked great and collected about 7 gallons every time the sump ran. A little more tinkering would have reduced the spill rate but wasn't worth the effort since I had something like 150 gallons of rain/sump water sitting in on my deck by this point.
Nice thing about it is that the 40-50 gallon rubbermaid containers don't look like rain barrels and come with lids for keeping things out of the water.
- Eric
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You are never beaten until you admit it. - - General George S. Patton