A small-scale wastewater cleaning plant is described that includes the key physical pretreatment steps followed by the chemical treatment of mud by flocculation. Water, clay particles, and riverside deposits mimicked odorless wastewater. After a demonstration of the optimization step, the flocculation process was carried out with iron(III) chloride and a cationic polyelectrolyte and lasted less than 10 s for 7 L of wastewater. This experiment is primarily targeted toward high school students to give a real world demonstration of solution and colloid chemistry, but is also useful for a more general audience. The demonstration has already been successfully presented to 700 visitors.