Super Mario Bros. Plumbing

Mario Brothers Plumbing (sometimes shortened to Mario Bros. Plumbing) is the plumbing business owned by Mario and Luigi, which, despite never appearing in the games, was featured in various cartoons and the movie. It is located in Brooklyn, in the neighborhood of Flatbush.

In The Super Mario Bros. Super Show!, it is located on the basement floor of an old apartment building, Mario and Luigi have succeeded in not only using the place as a workshop, but as their place of residence as well. As the basement is not a proper apartment, the brothers have learned to adapt to their surroundings, including the building's sneezing furnace and the garbage chute. Since the building is located next to the closed-off entrance of a subway station, anyone in the basement can feel the rumble of an incoming train.

The Super Mario Bros. Super Show!
Mario Brothers Plumbing was the setting of all the live action segments of the The Super Mario Bros. Super Show!. Here, Mario and Luigi interacted with their roommate Edison, as well as the resident monsters Clog, the Ratigator, and the CooKoo Bird; and in each episode, a celebrity guest star.

As mentioned, the old apartment also has a furnace which seems to have a life of its own (it sneezes) and it also has a Pizza Phone (originally a normal phone, but due to an accident, the pizza and the phone got mixed together), a periscope apparently able to see from Brooklyn even all the way to the Eiffel Tower in France, and a garden being grown in a bathtub with a living scarecrow.

The motto of the brother's plumbing in the show was "You clog 'em, we clear 'em" and they were said to be New York City's best plumbing service. A commercial bumper for "Neatness Counts" stated that their motto was, "The customer is always wet."

The Adventures of Super Mario Bros. 3
In The Adventures of Super Mario Bros. 3, Mario Bros. Plumbing only appears in the show's opening, where Mario and Luigi were looking at a photography album recalling the events of Super Mario Bros. 3.

Nintendo Comics System
Mario Bros. Plumbing made a small appearance in the Nintendo Comics System short story, "The Legend", which was a retelling of the Super Mario Bros. backstory. Here, the pipe that connects to the Mushroom Kingdom is clearly shown to be inside their home, and they responded voluntarily to the cries for help like in Super Mario Bros.; previously in the Super Show!, they were only said to find "the secret Warp Zone while working on the drain."

Nintendo Adventure Books
Mario Brothers Plumbing, also referred to as their plumbing workshop or simply the shop, is depicted as the home of the Mario Brothers in several stories. By the events of the first story in the series, they had the "Mushroom Kingdom Network System" installed on the eastern wall. The Mario Bros.' communication system consists of an advanced network of computers, radio telescopes, homing pigeons and TV monitors (an improvement over having to listen for Princess Toadstool's voice through one pipe).

Super Mario World television series
A Brooklyn apartment presumed to be the Mario Brothers Plumbing building appeared once in the Super Mario World animated series, during a flashback in "Rock TV", where Mario and Luigi remembered an outlandish phone bill for the "Speak to Santa Hotline", which presumably lets users talk to Santa Claus.

Super Mario Bros. film
In the Super Mario Bros. movie, Mario and Luigi's business is in their home and they simply stay in their house until they get business calls. In this portrayal, they own a white van with "Mario Bros. Plumbing" written on the side of it.

Super Mario Maker
In the official course "Did Somebody Call a Plumber?" in Super Mario Maker, the course begins with a Brooklyn setting, with the first two Warp Doors leading to what appears to be Mario Brothers Plumbing.

Trivia

 * Concept art from The Art Of Super Mario Odyssey seems to imply Mario Brothers Plumbing was originally going to appear in New Donk City.