Kusari doi – the Japanese characters are 鎖樋 which translates literally as “chain gutters” – are known in English as rain chains. They are used in Japan as downspouts to direct rain from a gutter to the ground, where it either flows into a gravel or pebble bed or into some sort of catchment.
A beneficial attribute from the ring rain chain is that it allows you to see the rain water travelling down the length which is normally hidden. Description from monarchrainchains.com. I searched for this on bing.com/images