DIAGNOSIS The dock's vacuum channel for sucking waste water is partially blocked or the rubber seal around the washing plate isn't tight.
FIX Clean the grey rubber gasket that rings the mop washing area in the dock. Wipe the small square suction holes on the washing plate. Ensure the dirty water tank is fully seated and its filter is clean and dry.
IF THAT DIDN'T WORK The drain pump in the dirty water tank compartment has failed. You'll hear no gurgling sound at the end of the wash cycle. This requires dock service.
HEADS UP Standing water under the dock promotes mold and can damage your floor. Always check for and dry any residual water after each wash cycle until resolved.