Basically, the glitch (now patched) involved joining a party while being in your own dungeon.
You would use a "stall" (teleing) with the account with 80+ dungeoneering, and the account you were leveling would click Join party, and the staller would continue to teleport, so the "party joining" was delayed.
The exp gainer would then enter his own C1 F1 small dungeon, complete it, and then the staller would change the floor to his higher (40+ lets say) and c6, the exp gainer would leave the ladder and get like 40k-150k exp for completing a f1c1 small.