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ASA slow pitch -- with 2 strikes, batter out on any foul ball or foul tip (as defined by ASA rules -- i.e. directly to hand or glove, not higher than batter's head, and caught); less than 2 strikes, a foul tip is a strike just like a foul ball and the ball is dead since it's slow pitch; if the ball is popped up over the batters head (e.g. behind the catcher) with less than 2 strikes, the batter is out if the ball is caught. With 2 strikes it's an out regardless of if the catcher drops it or catches it.

USSSA slow pitch -- technically, you only get 2 strikes, so the batter already is struck out in your situation. Assuming only 1 strike, a foul tip (as definined by the rules) on stike 2 is a strikeout. If the catcher drops the ball, it's not a foul tip, just a foul ball (in USSSA, a "courtesy foul" so to speak -- now the batter would have one strike and one foul, so the next foul would be a strikeout). With one strike on the pop behind the catcher over the batters head, the batter is out if caught by the catcher. If not caught, this would be the batter's courtesy foul.