Very simple - 3 guys in a party, one is leader and other two guys are the 80y and the powerleveler(low lvl). Once those two (powerleveler and 80y) go in dungeon, the low level (powerleveler) mobtags the elites (skullmob), then both leave party - high level kills it and low lvl player gets alot of exp, i mean ALOT!:D
You need 3 players to do this, if you try with 2 players hence the powerleveler and 80y, you will be kicked out of dungeon in a 1min to graveyard. So you get the 3rd guy who ''keeps'' the group and reinvites you when you leave group to kill elites (skullmobs). Basicly from fresh level 1 to level 50ish you can get in 8+hours if you know your stuff well AND THAT IS BANNABLE. Just inspect some fresh level 80ies around, you will see that their total quests done arent even 400, but mobs killed 40k plus, THERE ARE SO MANY PEOPLE THAT ARE DOING THIS AND GETTING AWAY WITH IT.