There are two ways to do this.
One way is to sneak into the men room instead of the ladies room. You'll have to carefully climb the toilet stalls into the vents without alerting the biologist who is reserving the center stall, where the vent is above and behind him.
Another way is to enter the break room through the ladies room, and before making a mess, climb into the vent above the refrigerator that takes you to the men room. You can then attempt to sneak past the biologist below when you exit the vent.