Down the Hatch is episode 17a of Rocko's Modern Life. In this episode Spunky swallows a Fatheads vitamin pill, and Bloaty and Squirmy believe that they have discovered an ancient and mysterious object.
The episode first introduces the television show The Fatheads on a commercial with Fatheads chewable vitamin pills. Heffer is seen watching the commercial in Rocko's house and goes upstairs to wake up the wallaby in surprise. Rocko quickly gets up to get ready for work. He says good morning to Spunky and deep down the dog's system, Bloaty the tick and Squirmy the ringworm are seen riding a boat, with the tour guide as the boat driver, through the colon. They approach the digestive system in the process.
Back at Rocko's house, Heffer swarms through the cabinets of the kitchen and comes across a jar of the Fatheads vitamin pills. He eats some and goes in the living room to watch television. When Spunky stare at Heffer, the steer feeds the dog a vitamin. But Rocko comes down and tells Heffer the time that he was at his grandmother's house and a cat exploded after swallowing a Fatheads chewable. Realizing what Spunky just did, Rocko and Heffer quickly become horrified and take Spunky to the vet.
Back inside the dog's digestive tract, Bloaty and Squirmy end up in turbulance while riding the boat (due to Rocko shaking Spunky at a desperate attempt to compel the dog to cough out the vitamin) and end up on land. They come across the Fathead chewable and believe that they could make a fortune with it. The tourist tells them to check out the boat so he could use the vitamin for his own greed. When he kiss it, he explodes instantly. Bloaty and Squirmy return with the boat to find that the tourist is missing. Bloaty initially think the vitamin is cursed, but Squirmy dismisses it, claiming it'll make them rich.
Back outside at the pet hospital, Filburt is coerced to give away his loaf of bread when he is offered a jar of sauce. He walks out, only to bump into Rocko and Heffer, who are taking Spunky to the pet hospital, the impact of which causes the turtle to drop and break the jar of sauce. Rocko apologizes and promises to replace it as he and Heffer then go to the doctor, who runs some tests on Spunky.
Inside Spunky's ear, Bloaty and Squirmy introduce the other parasites to the vitamin. They try to convince the people to pay to get their picture taken with it, but they refuse. The two friends use a hook, claiming the vitamin is the secret to eternal youth, causing parasites to come visit the supposed monument. While the judge comments on their greed, a few of the parasites break off some chunks of the vitamin to gain immortality, only to explode. Eventually, the judge and an angry mob appear before Bloaty and Squirmy, angered at the two for keeping eternal youth to themselves and forcing the rest of them to pay admission. Despite Bloaty trying to convince them, the mob storms over them and gobbles up the vitamin. When the doctor finds the vitamin in Spunky's ear, the parasites all end up exploding one by one around Spunky's body. Rocko feels relieved and hugs Spunky.
Back in the dog's body, Bloaty and Squirmy find that they are now alone, convinced that they really were cursed - with greed. They ends up holding hands and skipping away together as the episode ends.