What is an upper decker?

An upper decker is a prank that involves defecating in the tank of a toilet instead of the bowl. This causes the toilet water to become contaminated with feces and creates a foul odor every time the toilet is flushed. It is considered a highly disrespectful and unsanitary prank and is often done as a form of revenge or vandalism. The act can cause significant damage to the plumbing system and requires thorough cleaning and disinfection to rectify. It is not recommended to engage in such behavior.