It first appears during the school assembly, where Melvin introduces it as his latest invention. However, chaos ensues when George and Harold sabotage the Turbo Toilet 2000 by reprogramming it to shoot out toilet papers. However, Melvin knew of George and Harold's involvement, having set up a recording device, and turns over George and Harold to Mr. Krupp, who angrily puts them in separate classes for the rest of the school year as punishment for their pranks.
When Professor Poopypants becomes the new science teacher, he finds himself as the ridicule of the entire school because of his silly name, but notices that Melvin's brain is incapable of having fun. Deciding to recruit Melvin to his cause, Poopypants uses his machinery to enlarge the Turbo Toilet 2000 as part of his plan to get rid of laughter due to the fact that people have made fun of his name for years.
Using the school cafeteria's rotten leftovers as fuel for the robot, Poopypants directs the Turbo Toilet 2000 to take over the town of Piqua and turn everyone into zombies. After getting the Turbo Toilet 2000 to dispose of Underpants by swallowing him whole, Poopypants gets the Turbo Toilet 2000 to turn George and Harold into zombies, but their sense of laughter prevents them, causing the Turbo Toilet 2000's computer to crash. With that in mind, the Turbo Toilet 2000 shuts down, freeing all the citizens from Poopypants' control, and allowing Underpants to escape after gaining superpowers from the leftovers in order to defeat Poopypants for good.