Player 1: Run across to the horizontal panels in the upper right-hand corner of the room and set your entrance portal at the bottom and your exit portal at the top (this is important). Press the nearby switch and then quickly fire off the EXIT portal on the slanted wall to the left. Now watch as your colleague gets flung over the acid water, to the other side.
Player 2: You need to replace the portals used by player 1 in the same manner (entrance portal at the bottom and exit portal at the top) and once they’ve jumped into the infinite loop, hit the switch on your side and then immediately set the exit portal on the slanted wall in the corner. Once you’re both on the same side, just walk into the exit elevators.