You and a player from the opposing team press the button in 
front of you at approximately the same time, at which point 
both elevators elevate to the above arena to do battle. This
method eliminating the jump-system often used in mulch_dm
and other variants. Also, no need to fear pre-priming as the
grenades will only be refreshed as you are elevated into the 
arena. In order to return to your base, just shoot either of
the team signs that are up above the arena ground, and drop
into the escape hatch in the middle. The portal behind you at 
the main base teleports you to the spectator box.