While jellyfishing in Jellyfish Fields, SpongeBob and Patrick encounter an object sticking out of the ground. They decided to dig it up, and they discover an old submarine. Meanwhile, at the Krusty Krab, Squidward and Mr. Krabs think of an idea to bring the Krusty Krab to the customers. SpongeBob and Patrick drive the submarine into the Krusty Krab, which gives the idea to Mr. Krabs to have SpongeBob and Patrick take the submarine and sell Template:Data:Links to any passersby. Seeing this, Plankton gets upset since he had the idea years ago. He takes the fist of the Chum Bucket and uses it as a mobile Chum Bucket.
SpongeBob and Patrick are unsuccessful with their first customers, so SpongeBob offers to pay them to take the Krabby Patties, which they agree to. Meanwhile, Plankton attempts to sell food to a child, whom he then insults out of impatience. All of a sudden, the child's parents, great grandmother, and various other fish start throwing rocks at Plankton. Soon, the mob runs out of rocks, but since Patrick was not paying attention to the Krabby Patties, they burned and hardened. SpongeBob and Patrick are able to sell the burnt patties to the mob for them to throw, and the two friends head off.
Later on, SpongeBob and Patrick fall into an abyss and wake up a ginormous sea monster who has been asleep for the past 79 years. Starved after his hibernation, the monster purchases 640 Krabby Patties. However, just as SpongeBob and Patrick are running out of patties, Plankton's Chum Bucket vehicle comes crashing into the submarine. Chum squeezes through the cracks of the submarine, so SpongeBob and Patrick decide to use the chum to make the burgers, which the monster ends up enjoying even more than the Krabby Patties. Plankton sees the sea monster hand SpongeBob and Patrick giant dollar bills in exchange for the chum burgers, and he attempts to get the monster to refuse the food. However, Plankton is mistaken for a chocolate éclair and the monster chases him away. Meanwhile, because they are down in the abyss, SpongeBob and Patrick have to let go of all the money they have earned to float back up to the surface. Instead of money, they bring back 37,000 pounds of decorative undersea rocks, much to Mr. Krabs' disappointment.
The con man from "Chocolate with Nuts" returns in this episode and cons SpongeBob and Patrick one more time, this time without even trying, as they hand him money for trying some Krabby Patties. It seems like he remembers SpongeBob and Patrick since he says, "Hey, thanks again, guys."
Plankton's line "Someone should put you in a box, floating down the river, grandma!," has become a popular meme on YouTube, due to how insane the roast is.
Jack M. Crazyfish, who first appeared in "Blackened Sponge," can be seen hurling things at Plankton. His voice sounds different in this episode than in his debut.
The sea monster is voiced by Gene Simmons, who is well known for being the bass player for the band KISS.
The mother who is insulted by Plankton is voiced by Simmons' partner, Shannon Tweed.
In a way, SpongeBob and Patrick helped the Chum Bucket more than the Krusty Krab because the sea monster preferred Plankton's chum over the Krabby Patties.
SpongeBob confirms that the Krusty Krab does not have desserts on the menu.
When the monster mistakes Plankton for dessert, he breaks the fourth wall by looking at the screen and saying, "Now that looks like dessert to me!."
If counting this episode segment and its sister as one episode instead of separate segments, the previous and next episodes are both specials in between this episode.
In the Welsh dub, this episode is called " Crancdy'n Crwydro," which translates to "Spraying Crab."
Cultural references
The title is a spoof of Jules Verne's classic novel 20,000 Leagues Under The Sea, which revolves around its characters traveling the ocean in a submarine and encountering strange creatures.
The novel is also referenced in "ScavengerPants".
SpongeBob saying, “Bye Squidward” twice was most likely a reference to the film Blazing Saddles.
When Patrick says, "Ringo" this is a reference to former Beatles drummer Ringo Star.
There is a short distance between the grass in Jellyfish Fields to the submarine stuck in the ground, but later, the grass does not appear.
In addition, it is shown in numerous episodes there is not any grass around SpongeBob, Squidward, and Patrick's houses.
As SpongeBob and Patrick are running away from the jellyfish, SpongeBob's left shirt sleeve is not colored in for a split second.
Usually the series is shown that any underwater creature is much smaller than anything on the surface, but in this episode, it is shown that the submarine and the human skeleton are the same sizes as SpongeBob and Patrick.File:20,000 Patties Under the Sea 010.pngRight glasses
In the Krusty Krab, in one shot, the cashier boat is floating, but it is on the ground in the next shot.
When the sea monster takes the submarine off his head, the periscope at the top of the submarine is missing.
When Plankton says, "Ah, who needs that old rust bucket anyhow?" his voice is out of sync with the animation.
Running gags
SpongeBob drives the submarine and bumps into the Krusty Krab, destroying the front window.
