Fill the Tube
Siphon by filling the tube completely with water. Make sure there is no air trapped in the tube.
Make sure that the equipment itself and your hands are clean! You can fill the hose by dipping it in the aquarium water.
Do this only if your aquarium is large enough to accommodate the hose and not spooking the fishes out.
If your aquarium is too small to do this, try placing one end of the tube in the tank. Draw water on the other end by putting your mouth and sipping the water but not drinking it!
It will take practice but its really easy when you get the hang of it.
This should start the water flow.
Bucket Lowered
Make sure the bucket end is lower than the aquarium. If not, this process will not work.
If you filled it in the aquarium, plug one end of the hose tightly with you thumb.
Lift it from the aquarium. Then bring it lower than the aquarium to the bucket.
Thumb Off
Take your thumb off of one end and the water should begin to flow rapidly from the aquarium into the bucket.
You can control the water flow by pinching or folding the hose.
Discard
Discard the water in the bucket.