Charcoal filtration will work, but I don't know how big of a filter is needed. I suspect it has to do how much chlorine you have. So..
I don't know.
Exposure to air also allows the chlorine to escape, but that involves standing water for 24 hours. It gets away from your concept of open the drain and turn on the fill.
Aquariuim fish can take a 10% change directly with tap water, and eels are a bit tougher. I just don't now where the limit is.