Some habits never change.
A colleague recounted she was in the Times Square shopping mall and went to the washroom for a pit stop.
When she came out of her stall she saw an attractive, well dressed mainland Chinese woman come out of her stall, but did not wash her hands.
Instead she horked a large clump of spit into the sink and was on her way out the door.
My colleague was horrified and told her in Putonghua that it was not sanitary and that she should rinse the basin.
"But there's no water," she said.
My coworker then ran her hand under the tap to show that that the water was activated by motion detectors, but by that time the woman left the washroom.
So -- just assume every other public washroom in Hong Kong is dirty -- you never know who has just been in there.