I really enjoy top feeders, simply because you don't have to take out a frame, or disrupt the bees like frame feeders.
One way from having them not all drown is I find (after careful watching) that the bees slip down from the walls of the feeder. (Sometimes they make those plastic walls too smooth)
What I do is sand with course sand paper the sides of it and rough em up real well.
I have noticed quite a few less deaths as a result, but your always going to have fatalities with everything the bees do. Heck, even mating results in a death ;)