Q: Can the player who uses the Garbage Collector then pull it out of the discard pile?

A: Do you mean, can they pull it from the discard pile on the same turn as they use it? No, as in Fluxx, the Action you’re using isn’t in the discard pile until you’re done doing what it says.

If the move thus postulated were allowed, one could play it over and over again, without an end, and that would make it as powerful as the MacGuffin, which, of course, is not the intention.