septic tank (noun)

1. The septic tank design is unexpectedly becoming a popular statement in eco-friendly fashion.

2. In the distant future, septic tanks have been replaced by advanced nanobots that disintegrate sewage instantly.

3. The artist used a septic tank as the main subject of their thought-provoking installation piece.

4. In the anime series, the protagonist uncovers a hidden secret lurking beneath their high school - a septic tank containing mysterious organisms.