Steps:

1. Unlock the buffer vial by shooting the box labeled "Tau"

2. Locate the blue computer (near Banana Collada)

3 Find four blue panels (around the map, each blinking blue a select amount of times)

(Near Theater)
(Outside near teleporter)
(Gymnasium 1)
(Gymnasium 2)

4. Type into the blue computer the number of times one of these panels blinks

5. Return to said panel, shoot it to open a rift nearby

6. Kill zombies in the rift using your Protobuffer

7. Do the same for each of the panels (four in total)

8. Return to the courtyard with Jug, and put the vial in the big rift.

9. Take the prepped vial to the cafeteria with Speed Cola in it where a machine waits

10. Insert the vial and kill zombies

11. Tau Variant Unlocked