iRobot Roomba Combo Owner's Manual page 19

If tanks are ready for cleaning and LED indicators are not on:
1
Attach mopping pad to robot.
2
Return the robot to the dock and press the Clean button on your robot.
EN
IMPORTANT: Only certain cleaning solutions can be safely used
with your robot. A full list of compatible cleaning solutions can be
found on http://answers.irobot.com/s/roomba-combo-cleanser
or by visiting the app. Please do not use other cleaning solutions or
bleach-based products.
18 For more information, visit global.irobot.com
Pad Washing
At the end of a cleaning job, the dock will wash and dry the mopping pad. The
robot will lower the mopping pad and drive back and forth over the Pad Washing
Roller. This process will take several minutes.
IMPORTANT: Do not interrupt the robot while Pad Washing is active.
It is normal to hear noises throughout this process as the dock spins
the Pad Washing Roller and fills/drains the Pad Washing Basin.
Once complete, the dock will proceed to dry the mopping pad by blowing air.
NOTE: The drying process will last for a few hours. You may hear a
low hum coming from the dock while the dryer is active.
Visit the iRobot Home app to manually start or stop Pad Washing and Drying or to
customize pad washing settings.