To make it all a little more self-maintaining it would be easy to screw the clean-out plug in finger tight, mark the bottom of it, drill a 3/23" hole near the edge insert a piece of #14 solid copper wire and use pliers to put sharp bends in both ends. You want the end sticking out to be a bit long.

The wire should just about fill the drilled hole so the first-flow storage is self-draining while maximizing water capture. When/if the drain hole gets plugged with sand and crud you can simple wiggle the wire sticking out to restore flow. After a while you will have to remove the plug to clear the mud and crud so it stays self-draining but not every time. In this case extra convenience translates into more utility.