In the original Ratchet & Clank, it can be found by Clank while exploring outside in space in the Blarg Tactical Research Station in Nebula G34. In the 2016 re-imagined Ratchet & Clank, it is found on Aridia instead, after traversing an area with the Swingshot inside Skidd's Sports Shack.
The Hydrodisplacer can drain and fill pools of water by interacting with water plug points, allowing Ratchet to clear or fill a pool depending on which is required to progress. The volume of water that can be contained within a Hydrodisplacer is 50,000 liters, far greater than the gadget's external volume may have indicated, and uses quantum compression technology to manipulate water particles and place them into a compression tank.
Behind the scenes
The Hydrodisplacer used to look much different than the final version. The early Hydrodisplacer is seen in the profile picture, while the one found in the actual game is seen in the smaller picture.