Actor Allusion: Peach, played by Allison Janney (more famous for playing C.J. Cregg on The West Wing) announces that the dentist is about to do a root canal, bringing to mind the hilarious West Wing episode "Celestial Navigation".
There are a couple of allusions (the song "Beyond the Sea" and the line "That's my boy.") to Albert Brooks in My First Mister
What Could Have Been: A deleted scene had Nemo making it through the sewage treatment plant. While this would have explained the question raised by the scene's absence, it was cut, possibly for being too frightening.
According to the DVD commentary, the director cut the scene for two reasons: First, it put too much more focus on Nemo- as Marlin is the main character of the film. Second, it didn't add anything that the rest of the movie hadn't already done; making it just a repeat of the filter scenes.