From the Super Mario Wiki
The Hydrogush 4000 is a big yellow machine invented by Professor E. Gadd in Mario & Luigi: Partners in Time that spews water, much like F.L.U.D.D. (another one of E. Gadd's inventions, seen in Super Mario Sunshine). Its appearance looks just like F.L.U.D.D.'s "head," where it sprayed out water; however, this machine is a bigger version of that on wheels, and with a hose coming from its mouth. Due to its large size it is capable of producing vast amounts of water.
In Mario & Luigi: Partners in Time, the younger E. Gadd's laboratory, located on Thwomp Volcano, is about to be destroyed due to the volcano erupting. So the older E. Gadd, from Princess Peach's Castle, sets up the Hydrogush 4000 and sends the water to the volcano through a time hole to keep it from erupting, thus saving younger E. Gadd's laboratory.
At the very end of the game, it is discovered that baby tears can be used to counteract the Shroobs. Professor E. Gadd alters the water's chemical makeup to be the same as the babies' tears. The machine spews water all over the Mushroom Kingdom of the past, ridding it of every trace of the Shroobs (except the ones captured by the Koopa Troop and held in Bowser's Castle).
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