From the Super Mario Wiki, the Mario encyclopedia
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, was set on fire due to the volcano erupting. After the younger E. Gadd sees Baby Mario putting out a fire, the older E. Gadd, from Peach's Castle, realizes his youth memories are being rearranged, and then sets up the Hydrogush 4000 based on his new memory, sending a torrent of water to the volcano through a time hole to stop the eruption, although enough damage was done to render the lab unusable. With the volcano inactive, the Mario Bros. are able to enter it, although not without a battling an angry Mrs. Thwomp, who has been waiting with her husband Mr. Thwomp for the short-lived eruption.
At the very end of the game, it is discovered that baby tears can be used to counteract the Shroob Mushrooms. After receiving the information from Stuffwell, Professor E. Gadd alters the water's chemical makeup to be the same as the babies' tears. The machine then spews water all over the Mushroom Kingdom of the past, ridding it of every trace of the Shroob's invasion.
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