Bathroom fold down sink stopper, Hymer Sunlight2

[Ken Allan]

Greetings,
Bought a 2018 Hymer Sunlight2. The toilet/sink is in the rear. It has tray for washing that folds up and drains into a compartment that has a drain plug. It appears there should be a bracket that opens the drain stopper when I pull the tray down and closes it when the tray goes up. I cannot find any info on manufacturer of this tray.

Does anyone know the manufacturer OR have any information on this drain (or how it works)?

Thanks,

Ken