after washing the mop, the dock doesn't suck up all the water, leaves a wet patch underneath.

Diagnosis

The presence of standing water on the mop washing tray of the Roborock S8 MaxV Ultra typically indicates a failure in the vacuum-assisted drainage system. Unlike basic gravity drains, this dock uses a powerful suction pump to pull residual water from the tray into the dirty water tank. When a wet patch remains, it means the airtight seal between the tray and the suction manifold has been compromised, or the airflow is restricted, preventing the pump from creating the necessary vacuum to evacuate the remaining liquid. This issue is most commonly caused by the accumulation of "sludge"—a mixture of floor detergent, pet hair, and fine dust—that settles in the narrow drainage channels. If the grey rubber gasket surrounding the washing plate is slightly misaligned or coated in debris, air leaks into the system, effectively "breaking" the vacuum. You can confirm this by observing the dirty water tank during the final seconds of the wash cycle; if you don't hear a distinct, rhythmic gurgling sound and see air bubbles rising in the tank, the suction is insufficient.

How to Fix It

Follow these precise steps to restore full suction to your docking station:

1. Power down the dock and remove the dirty water tank completely.
2. Locate the grey rubber gasket that rings the perimeter of the mop washing area. Use a damp, lint-free microfiber cloth to wipe the entire circumference of this seal. Ensure no hair or grit is trapped beneath the rubber lip, as even a 1mm gap will prevent a vacuum seal.
3. Inspect the small, square suction apertures located on the base of the washing plate. Use a toothpick or a soft-bristled brush to clear any compacted debris from these holes. If they are clogged, the pump cannot pull water regardless of how powerful it is.
4. Remove the filter located at the top of the dirty water tank. Rinse it under lukewarm water until the water runs clear, then let it air dry completely. A damp or clogged filter creates backpressure that inhibits the suction pump's efficiency.
5. Reinsert the dirty water tank and press down firmly until you hear a physical click. An improperly seated tank prevents the internal valve from opening, leaving water in the tray.
6. Run a "Customized Mop Wash" cycle from the Roborock app to test the drainage.

If That Didn't Work

• Check for a "Air Lock" in the pump system. This happens if the dock was tilted or if the tanks were empty for too long. Fill the clean water tank to the max line and manually trigger three consecutive mop washes to force the pump to prime itself and push air bubbles out of the line.
• Inspect the base of the dock for physical warping. Place a level or a straight edge across the washing tray. If the dock is not on a perfectly flat surface, the rubber gasket may not make full contact with the tray, allowing air to leak in and preventing water from being sucked up.
• Perform a deep clean of the internal drainage manifold. Use a vacuum cleaner with a narrow crevice tool to suck out any debris directly from the drainage holes on the tray to ensure there is no hidden blockage deeper in the piping.
• Verify the dirty water tank float sensor. If the float (the small plastic piece that rises with the water) is stuck in the "full" position due to grime, the dock may prematurely stop the suction pump, leaving water behind. Gently wiggle the float to ensure it moves freely.

Heads Up

• Avoid using third-party cleaning solutions or highly concentrated soaps. Over-sudsing creates foam that the suction pump cannot evacuate, leading to permanent water residue and potential pump burnout.
• Standing water on the tray can lead to the growth of black mold and unpleasant odors within 48 hours. If you see a wet patch, wipe it manually with a paper towel immediately to protect your flooring.
• Inspect the rubber gaskets every 30 days. Over time, the rubber can lose elasticity or become coated in a film of detergent, which reduces the airtight seal necessary for the vacuum function.
• Ensure the dock is placed on a hard, level surface. Placing the S8 MaxV Ultra dock on a thick rug or uneven tile can cause the chassis to flex, compromising the seal of the washing plate.