You're able to farm floor 100 with your clan or friends over and over again by simply having 1 player leave before the final hunter is killed. The remaining players then proceed to kill that final hunter and then join up on the player that left to get to floor 100 again. Rinse and repeat.
Note - Players have to take the elevator up to floor 100 to actually aquire the checkpoint save unless they already have it. If they don't do this you risk resetting at level 1.
The final hunter always drops a named item and frequently drops exotics so you have to take turns with who leaves.