Drum Bathing

When the character has to take a bath inside a barrel or small oil drum that is usually outdoors and heated over a fire underneath. This is typically seen in poor rural environments out in the country. Despite the bath being too small to fit more than one person, Bathtub Bonding still can occur, but it's guaranteed to get cramped, making at least one of the bathers uncomfortable. Outdoor Bath Peeping is another thing that is generally guaranteed. This is the only time a bathtub can be outside without it being considered an Awkwardly-Placed Bathtub.

Examples of Drum Bathing include:

Anime and Manga

In the anime film Tenchi Muyo! In Love, Kiyone is seen in one just before being teleported out of it by Washu.
In Dragon Ball Z, Goku commonly uses one as the default bathtub at his house. One notable moment is in the Tree of Might film when he bathes in it with Gohan.
Seen in the fourth episode of Strike Witches 2. With two barrels right next to each other.
Kaede and Negi share a barrel in an early chapter of Mahou Sensei Negima.
Nanako bathes in a barrel at the end of the second episode of Amazing Nurse Nanako.
The ending of Mega Man 9 shows Dr. Light bathing in a barrel, with a reformed Magma Man providing the heat.
Near the end of Mirai Nikki, Yukiteru and Yuno take a bath in a oil drum together.
Zettai Karen Children: Mio bathes in one.
In Arakawa Under the Bridge, it's the only kind of bath available to the bridge-dwellers. A Modesty Towel is recommended, in case the police come by.
Keitaro is forced to use one (instead of using the Hinata Inn's hot springs) in the early parts of Love Hina.