Have a gander at the photo. You can some sort of water container placed to the left of the table with a box of tissues. This is not so that you can whip out your dolphin (which likes occasional dips in water) and engage in health care - wiping off with the box of tissues.
The tub of water is for folks to wash their glasses and does so with ultrasound (
source). You don't have to pay or feel obliged to buy anything.
Just stop by and dip your glasses in the tub for a few seconds and wipe off with the tissue - wipe your glasses I mean.
Unlike some shop assistants that I've seen in Malaysia who leech on to you, you will rarely be bothered by shop assistants when you use the ultrasound tub.