Fahr outpost is level 7, after the Poshley Heights level. Use the super jump in Rogueport square to make the giant treasure chest fall. The ultra hammer is inside. Now go to the Twilight Town pipe. Right before you go into the room, there is a concrete block. Bust it with the ultra hammer, and you've found the pipe to Fahr Outpost. Don't ask me where in Fahr Outpost it is, though- I'm still looking for it myself. Good luck- and let me know if you find it!