I personally swear by this contraption I got at Wally-World one day.  If I remember right, it's called a Python.  It has one end that connects to a faucet in your kitchen/bathroom, and the other end you stick in your fish tank (naturally).  The faucet-end has a bottom piece you can loosen for suction from the fish tank, and tighten to fill.  You just mush the other end around in the gravel, and it sucks up all the little nasty bits, then you can just lock the other end down and fill.  Works great, you'll never have to use a bucket again.