Yeah, I would hesitate in hoisting a five gallon jug in the slip in broad daylight. The rattle siphon is very easy, discreet and efficient. By having a towel handy when removing the siphon from either tank or jug, it is easy to do so without a single drop of fuel on boat or water. Of course, you wouldn't want to "top off" if there is the least chance of over-filling, but if the jug is mostly lower than the fuel fill opening during transfer operations, it will stop when levels match inside and outside. If I needed 100% tank capacity before a long passage, I would probably stop at a fuel dock, or carry a full fuel jug for transfer later.