Python. Put the narrow (exit) end in the toilet. Not underwater in the toilet, just over the rim and drop the lid down on top of it. Put the wide end in the aquarium underwater upsidedown (kind of at an angle) so it fills with water. Lift it up out of the water (upsidedown, sucking side pointing straight up), water will start flowing into the narrow tubing, as soon as the siphon starts, put it back in upsidedown at an angle fast so that it fills back up with water and doesn't suck air, then go to work!
Sounds complicated, but once you figure it out it makes complete sense. Easy easy easy! No sucking, no pumps, no buckets, everything goes right down the toilet. Just don't suck up anything you don't want to!
It's all in the timing and there shouldn't be any water in the tubing to start with. It'll still work with water in the tubing, but it's harder to start, you may have to lift the wide end way up over your head to get the siphon started.
If I'm feeling really lazy when it comes time to fill, I'll mix saltwater in my storage tank (read: 55 gallon garbage can on wheels $35 at home depot), hook a big powerhead up to a piece of hose (or python), drop it in the garbage can and turn it on.
Enjoy,
~Todd