The detention bucket is a small (maybe 2 gallon?) bucket with a screen at the top. It helps control the water and get it to one of two places: Into the rain garden, or under a super-downfall or in the event of a blockage, into the sewer as normal. It is filled with concrete to keep it from blowing around, and connects to a PVC pipe that is buried under my front yard (not to scale - it's 20+ feet to the sidewalk) and that pipe empties onto the sidewalk. Water flows across the sidewalk and into the rain garden, and if it manages to overflow into the street, dense groundcover will prevent too much erosion.
Whatcha think?