E.O.S has its own cleaning cycle. After you run it with an Aroma-Cup, E.O.S will require a cleaning cycle be run (you don't want residue of one oil to mix with the next oil you are making).
To clean, you simply put in clean water into the reservoir and push the button. The cleaning cycle takes less than 5 minutes. It removes all traces of oil from the previous cycle and is ready for a new Aroma-Cup.