How do I siphon my aquarium without a pump?
Siphon Pump With Vacuum
All you need to do is insert the siphon tube end into the aquarium, turn on the gravel vacuum, and let it do its job. Simply move the siphon tube along the gravel at the bottom of the aquarium to suck up dirt and/or to drain out water as you see fit. It really could not be any easier.