Toilet flush buttons

This question has been bugging me ever since I've started learning usability.

I am talking about the two buttons for the flush : Full and half container.

On one hand, the button shape has to represent its function. Thus a bigger button must mean the full container.

On the other, dangerous/heavy process triggers should be protected from being triggered by mistake and generally harder to trigger(If you press it, you mean it). From that point of view, the full container button should be smaller and further from the user and the half-container should be big and easy to reach/press.

Also, keep in mind, that I come from a country where water is scarce. So people are educated and encouraged from a very young age to conserve. But it's also a rising trend worldwide now...

While observing these interfaces all over the world, I didn't see any consistency in the matter. The buttons really go both ways. Sometimes the full container is the big one and sometimes it's the small one. It is inconsistent even within the country. I've also seen all kinds of unconventional designs. But again, nothing clear and intuitive from the moment you see it...

What are your thoughts on the matter? Have you ever seen a good, clear design, that is really intuitive? Do you know of any standards for this?

NOTE: Please don't suggest text as a solution. Icons may be interesting. But I've never seen a clear icon for that.