To keep the window well flooding it would be wise to use a length of hose attached to your outside water spigot. Direct the hose into your window well (be sure not to point the hose directly into the window as this will defeat the purpose of having the well flood) and give the knob 1/4 turn. If this is not a sufficent amount of water to properly flood your well increase the knob turns by 1/8 turn until the desired flooding is acheived.
As to clenliness I suggest that the lenght of hose used be sufficent to allow you to hide it from view within the garden or behind bushes. Remember neighbours don't like to see unsightly hoses laying about your yard. You could go so far as to bury your hose underground but be sure to bury it below the frost line since you won't have the desired flooding of the well in the winter.
I also suggest you get a spigot splitter so you can flood your window well and water the lawn at the same time.