Tank is introduced as a slow and hopeful tortoise in the episode May the Best Pet Win!, and he is named only after being picked by Rainbow Dash as her pet. He is introduced in Fluttershy's backyard along with many other animals, where Fluttershy states he had always dreamed of being somepony's pet. When Rainbow Dash begins searching for a suitable pet, Tank makes many attempts to get Rainbow's attention but to no avail. Still, Tank persistently attempts to get Rainbow Dash to choose him as her new pet, but she refuses, seeing him as a useless, slow pet that will only "keep her grounded".
Despite her initial rejection, Fluttershy convinces Rainbow Dash to let Tank participate in the competition, if only for the sake of convincing Rainbow that if she gives him a chance she'll end up liking him. He is not considered pet material at first by Rainbow, as he is slow and cannot fly, but he wins her over with his tenacity. He is the only animal that helps Rainbow Dash after she gets caught in a rock slide, and gives her a ride on his back to safety. She chooses him as her new pet over the falcon that originally won, since he was the only pet to cross the finish line with her, as she had requested.
In the final scene of the episode, Tank is seen flying around with a magic-propelled helicopter rotor strapped to his shell and wearing aviation goggles, allowing him to keep up with Rainbow Dash and follow her in the air. The design of the shaft of Tank's helicopter-like flying machine has been used for background weather vanes in previous episodes.
Tank appears in one scene of Too Many Pinkie Pies, inside Fluttershy's animals' tree hiding spot.
His next appearance is in Just for Sidekicks. Spike offers to look after Tank for Rainbow Dash while she is in the Crystal Empire. At first, Rainbow is reluctant, claiming that Tank can look after himself, though he immediately proves her wrong by crashing into several things and knocking his rotor off. Throughout the scene, Rainbow acts as though the 'relationship' between her and Tank is strictly professional, but she gets embarrassed when the tortoise gives her a long lick on the face (witnessed in full by Rarity). Later, in the library, Rainbow and Tank share a quick nose rub while they think no one is watching.
Before she leaves for the Crystal Empire, Rainbow suggests that Spike should at least think about getting a helmet, because "You only want to get hit in the head by a flying turtle... once." Spike ignores the advice, and Tank flies into his head several times in the episode, knocking him out the second time, and only after the third time does Spike learn his lesson and wear a crash helmet.
On the train to the Crystal Empire, Tank joins the other pets in taking out Joe's refreshment trolley, and munches on a spilled donut.
Tank interacts with some of the other main characters' pets all through the episode. Opalescence seems to show affection for him, first rubbing herself against him in Carousel Boutique, then lying on him in the train, and spinning round and round by clinging on to him near the end of the episode. He attempts to land on Owlowiscious's perch, inadvertently catapulting the owl across the room, and Angel kicks him through a door to open it, leaving him spinning upside-down like a spinning top.
In Magical Mystery Cure, Tank appears in one of Rainbow Dash's flashbacks.
He also appears briefly in the background with Rainbow Dash in Pinkie Pride. In the episode Maud Pie, Tank is seen with the other pets while the Mane Six and Maud Pie have a lakeside picnic. Tank also appears in Testing Testing 1, 2, 3.
Tank appears again in Tanks for the Memories, where he starts showing signs of sleepiness in preparation for hibernation through the winter. Rainbow Dash, having made plans with Tank during the winter, tries numerous ways to prevent winter from coming so Tank doesn't hibernate, but each one fails. Eventually, Rainbow tearfully gives in and lets Tank sleep until spring.
In Do Princesses Dream of Magic Sheep?, Rainbow Dash polishes Tank's shell at Carousel Boutique during the Mane Six's pet grooming day.
In Applejack's "Day" Off, Rainbow Dash wears the matching slippers that represent Tank from Tanks for the Memories appears again when she waits her turn at the Ponyville Spa.