If you have been using something like a gravel vacuum and bucket to do your water changes because you can't connect a water-flow control valve to your sink faucet (and at this point you've probably exhausted yourself), or perhaps your home doesn't have the best water pressure, or you don't want to waste as much water as with a typical water-flow control valve than what I am about to show you is a super simple solution and a total game changer!
Say goodbye to buckets and buy yourself a pond pump and enough hosing (that will fit onto your pond pump) to reach from your sink, bathtub, etc to your aquarium (and you may want something to hold your hose in place.. like a clamp or heavy object).
How-To
Connect the hose and pond pump together. Set the pond pump into your aquarium while the other end of the hose goes in the sink drain. Plug in the pump and the water will remove the tanks water and go down the sinks drain.
To fill the tank back up you adjust your sinks water temperature as needed, close the sink drain (so it will continuously fill with water), and leave the water running (traditional sinks usually don't overflow as they have a top drain hole). Place the end of the hose into the aquarium and then plug in the pump by the sink and place the pump into the sink of continuously running water.
Once the tank is filled with clean water unplug the pond pump (assuming it doesn't have an off/on switch like mine), place your finger over the end of the tube in the tank and bring it to sink to drain out any excess water in the tube.
To fill the tank back up you adjust your sinks water temperature as needed, close the sink drain (so it will continuously fill with water), and leave the water running (traditional sinks usually don't overflow as they have a top drain hole). Place the end of the hose into the aquarium and then plug in the pump by the sink and place the pump into the sink of continuously running water.
Once the tank is filled with clean water unplug the pond pump (assuming it doesn't have an off/on switch like mine), place your finger over the end of the tube in the tank and bring it to sink to drain out any excess water in the tube.
Additional Tips
Pond pumps don't really have a lot of suction when pumping water so you probably won't have to worry about fish, gravel, etc getting sucked up into these vents. If you are worried about small fry, etc getting into the pump than you can try placing the pump device into some panty-hose (or other fine fabric that water can easily travel through) and knotting off the fabric around the pump.
Be sure your sink or tub is clean before filling it with water (vinegar is one of the best natural cleaning agents in my opinion) as sinks are one of the germiest places in the home (more so than the average toilet). You could also place a clean bowl inside your sink to place the pond pump in instead of having it set in the sink itself (which is probably the best way to go about this anyway), and this could also be beneficial if your sink doesn't have a top drain so that you don't have to worry about water overflowing and you could then leave the sink drain open instead.
I use the Tetra 140GPH Pond Pump, it comes with 3 different sized hose adapters (a 1/4, 3/8, and 1/2 inch ID) and has an adjustable flow rate (which gives off around 3 inches of head at its lowest setting and over a foot of head on its highest setting). Keep in mind the GPH when looking for a pond pump because that will control how fast you can get your water change/s done (with the 20ft vinyl hose I attach to this pump I can basically empty 1 gallon of water per minute).
I use the Tetra 140GPH Pond Pump, it comes with 3 different sized hose adapters (a 1/4, 3/8, and 1/2 inch ID) and has an adjustable flow rate (which gives off around 3 inches of head at its lowest setting and over a foot of head on its highest setting). Keep in mind the GPH when looking for a pond pump because that will control how fast you can get your water change/s done (with the 20ft vinyl hose I attach to this pump I can basically empty 1 gallon of water per minute).