This one always comes to mind when I see some fancy toilet designs at various venues. Which one do I press? Normally in UI a bigger button usually means a more used feature. I can't imagine the average person doing number 2 more than number 1. Most toilets around here have the same size button but an icon with a big circle representing a big flush and small circle for small flush. The buttons being the same size makes the icons have more "meaning".

I have just gotten used to that is not always the case and they actually went for small button = small flush. It makes sense physical-wise but UI-wise not so much.