As previoudsy mentioned the key to rapid filling is to tilt the tank slightly to facilitate air escaping as the tank fills. The tank can be filled with the cap off and then in the dark the reel inserted and then the top put on. Of course you need a room that can be used as a dark room.
However if you considered what happens during filling and emptying the following happens. During filling the film at the top of the reel receives a bit more contact time with the developer. However during emptying the reverse situation occurs. The two situations tend to cancel each other out. So don't worry.