You can use a siphon to drain any amount water from anything or to suck up any fish excrement etc i use it in my betta tanks to siphon the crap off the bottom then i just fill up with clean de-chlored water
I've found if I put the large siphoning end in the tank so that it is full of water, then I either use my mouth to get the flow started or I use a turkey baster, since the end is just a little smaller than the tubing and fits quite nicely.