Even with the K'funs I don't do that.
Kayfun Lite: I use the fill-port under the base. Remove the screw and fill directly thru the stock blunt nozzle of my 30ml bottles. No, nothing with the air-hole.
Kayfun 3.1ES: I use the fill-port on the side of the base. It's a one way valve. And very effective at that. I just use a needle tip bottle to fill directly thru that valve. No, nothing to do with the air-hole on this too.
Erlkonigin: Use any bottle you like. Just loosen the drip-tip, turn the top lid 45º, fill-ports will be visible ~ fill with a pointy tip bottle directly. If you want to use a blunt tip bottle ~ just remove the dry-tip (b'coz the drip-tip will restrict the placement of the bottle's girth). NOTHING ELSE to do. No turning upside down (like the Aqua), no blocking os air-holes, whatever. Just FILL from Top and it will not flood the chamber. Some ingenuity indeed!