Gutter Drain Control Valve
This is designed to fit a standard home 2"X3" gutters. There is a small gap around the valve which allows a small amount of water to drain around it to keep the drain cleared out. 95% of water flows past it and in the direction that you want. A hole in the handle allows you to use a hook from the ground to adjust the valve as needed.
You will need to remove the drain, cut the tabs off of the gutter, install the valve then install the drain. This is a simple install for any home owner.
$14.99 each + $8.00 shipping up to 4