Like any item with moving parts the click-clack in your basin waste needs regular cleaning.
The click-clack can then be cleaned using soapy water only to remove any foreign matter. It is a good idea to clean the waste hole while the click-clack is removed. Limescale has to be removed regularly as it can cause the click-clack to cease.
Never use cleaning materials which contain hydrochloric acid, formic acid, chlorine bleaching lye or acetic acid as they will cause damage to the mechanism and invalidate the product warranty.
When replacing the click-clack and push button do not over tighten.