There is device that for changing water in aquariums called a Python.
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blurb states "The special connector fitted to a normal household tap creates a vacuum when the tap is turned on full pressure. (In this mode, the tap water goes to waste down the sink). This vacuum draws water from the aquarium through a gravel cleaner and into the sink. Once the required amount of water has been removed from the aquarium, the tap connector can be switched to allow the tap water to refill the tank through the same hose"The unit costs about £30 for what appears to amount to a bit of plastic (A standart gravel cleaner costs about £4.00)
Does anyone have any idea of how a DIY version could be acheived?