A toilet or dedicated utility/mop sink connected to the sanitary sewer is generally a better choice than a bathtub or kitchen sink. Before pouring it out, large pieces of hair or debris should be removed so they do not contribute to clogged pipes.
Dumping mop water into a bathtub can leave dirt, germs, and chemical residue on a surface people later use for bathing. Kitchen sinks should also be avoided because they are used around food and can become contaminated by dirty cleaning water.
Dirty mop water should never be poured into storm drains, streets, or natural waterways because those routes can carry contaminants directly into the environment. The safest option is usually a sanitary drain designed to handle wastewater, while following any local disposal rules for stronger cleaning chemicals.
