These episodes have quicksand scenes, and they always have a submersion. Any episode with a number that's a multiple of three is a sinking episode. A young female character is always the character who ends up sinking.
“Casey's Shell is a sinking episode of Rocko Squad Prime and is the third episode of the first...Casey's Shell
“Natalia Finds Trouble is a sinking episode of Rocko Squad Prime and is the third episode of the...Natalia Finds Trouble