One day in Bikini Bottom, SpongeBob wipes the grill with a sponge (made from part of his own tongue) at the Krusty Krab. He proclaims that it is freshly clean and tries to convince a customer to eat a Krabby Patty that was on the grill. When SpongeBob goes back inside to cook the patty, the customer asks Squidward why he does not want a Krabby Patty, and he replies that he has seen what SpongeBob cleans the grill with. It goes back to SpongeBob, who is on his way to the freezer for a patty when he slips on a puddle of water. Upon closer inspection, SpongeBob observes that the puddle is coming from the sink, which is clogged with water. As he is trying to figure out how to unclog the drain, Patrick comes in and slips as well. He helps SpongeBob try to pull the drain plug.
Eventually, Mr. Krabs overhears them trying to pull the drain plug and stops them before they have a chance. He tells them the story of the Main Drain. He tells them that there was a plug that two kids apparently pulled long ago that ended the world of Bikini Bottom. When they ask him where it is, he becomes nervous and tells them to go away. The two go outside and SpongeBob steps on Plankton, and then they ask him about it. He becomes nervous as well and tells them to go away. SpongeBob says that he heard it from Mr. Krabs, and Plankton claims Mr. Krabs was lying. They ask him where it is they once again do not get the answer. They turn to Old Man Jenkins, but he yields no results.
They then go on an adventure to find the plug by dragging Patrick's house around. Just before they pull the plug, Mr. Krabs and Plankton stop them and tell the story of how they were the ones that pulled the plug when they were younger. They explain that they lied because they did not want SpongeBob and Patrick to look for it. Unfortunately, Patrick had already pulled the plug when they were telling the story and everything (including themselves and the Bikini Bottomites) is sucked into the drain.
Patrick then sits up in his bed, telling SpongeBob that everything was "the most realistic story he has ever heard," indicating everything that happened was only SpongeBob's story.
Running Gag: Patrick turning on music on his radio when Mr. Krabs is about to tell the story of the Main Drain.
Though it was revealed that this episode was only a story being read to Patrick by SpongeBob, the entire population of Bikini Bottom was sucked away before: in the episode "A Flea in Her Dome," everyone was sucked into Sandy's Treedome. This event could have been the inspiration for this story.
The Main Drain, which sucks in all of Bikini Bottom, obviously refers to the end-of-the-world scenario "killer strangelet."
Like his arms and legs, SpongeBob's tongue can also be detached and reattached.
It's odd with Patrick's antenna, in some episodes, it breaks quite easily, such as "Christmas Who?" with a bauble, but it can hold bubbles and a heavy rock with Patrick and SpongeBob on it.
This is the second time Mr. Krabs and Plankton were shown as friends and kids. The first was "Friend or Foe."
This is the third episode where Mr. Krabs warns SpongeBob and Patrick about doing something, but they do not listen to Mr. Krabs. The first being "Hooky," second being "Sailor Mouth," and the fourth will be in "Face Freeze!."
This episode reveals that SpongeBob is aware that Squidward thinks his life sucks as he added a scene where Squidward says, "Another miserable day..." in his story.
It was revealed in this episode when SpongeBob and Patrick are seen flying on Patrick's house intended with bubble made balloons. This scene of Patrick's house is very similar to Carl Fredricksen's house from the Disney/Pixar film Up.
When SpongeBob said, "Patrick we need to find that drain," the road suddenly disappears.
When SpongeBob put the danger sign on the floor, the lever beside the freezer disappears.
When Mr. Krabs turned off the lights, it is the left side, but when he finished the story, the switch suddenly changed positions. The next scene shows that the switch is above SpongeBob, hanging on the ceiling.