The difficulty of filming with water is why even big-budget films often choose to stay out of the water altogether, although that also comes with plenty of drawbacks. They have to rely on tricks like using fans and adjusting the frame rate to mimic the way water affects people’s hair, all while accepting that it still probably won’t look anywhere near as good as “Avatar 2.”
Considering that most sitcoms go their whole run without ever putting the camera below sea level, it’s impressive that “It’s Always Sunny” even tried it at all. Then again, “The Gang Goes to Hell” is already ambitious in every other way that counts: In run-time, character work, and even thematically. The whole second half is a homage to “No Exit,” a 1940s play where three people trapped in a room slowly realize that hell is not made up of evil demons or torture chambers, but simply of other people. Sure enough, the Paddy’s crew drive themselves insane purely by being around each other, deprived of any outside force to rail against. Even when they see a chance to escape the water, they still try to drag each other down.
The whole episode underlines the idea that these characters are terrible for each other, that they’re all harming themselves by sticking around, but much like when the characters of “No Exit” are faced with the ambiguous empty hallway, they all prefer the safety of their group than the unknown world outside of it. It’s a dark, surreal episode, and much of that feeling is evoked by the change of set. “At the end of the day,” Howerton concluded, “I was glad we had the tank.”