The pressure gauge is one of the 3 items needed to finish the quest Ernest the Chicken. It is needed to repair Professor Oddenstein's machine along with an oil can and a rubber tube, so he can turn Ernest back into a human.
This item is found submerged in the waters of the piranha-infested fountain in the south-western area of Draynor Manor. To get this item, the player must kill the piranha using poisoned fish food made from the poison (found in the witch's larder in the main floor) and the fish food (found in the 1st floor among the ghost). If you don't use poisoned fish food, the piranhas bite your fingers and cause 1 hitpoint of damage.
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