The "Flash Liquidizer Ultra Dousing Device", better known as F.L.U.D.D. or FLUDD and pronounced "flood", is a multipurpose water pack from Super Mario Sunshine. It was invented by Professor Elvin Gadd and is carried like a backpack. Since F.L.U.D.D. is able to converse with Mario, it's believed to be equipped with some kind of artificial intelligence. In Japanese it is just called a "pump" (ポンプ).
