Downspout Diverter for Rain Barrel (or to make a DIY) -
Rain Water Collection System Colander Rainwater Downspouts Diverter Connector Roof Water Diverter for Lawn Yard Rain Barrels Patio Watering Black - Walmart.com
Guide to Popular Rain Barrel Downspout Diverters
The Rain Barrel Water Saver" - True North Eavestroughing