A dirty water tank is the sink your robot mop carries around

A dirty water tank is exactly what it sounds like — a removable container that collects the grimy water after your robot mop scrubs the floors. Instead of pushing dirty water around or leaving it on the mop pad to re-spread, the robot separates the clean water it sprays from the dirty water it picks up, and you just empty the grimy tank when it’s full. It’s the difference between mopping with a sponge you rinse every five minutes and mopping with a sponge you dip once and never wring out.