In English, “American” by itself refers unambiguously to the United States of America because, (again) in English, there is no continent called “America.”
America uses flush toilets unless you’re on an airplane. Besides, we can clearly see a huge water tank, which is how flush toilets work.
Unfortunately not though, because “American” is already used exclusively in reference to the USA. There is no adjective to refer to things from the Americas collectively. One of these two possible uses is extremely common and the other is extraordinarily rare. If you need the rare option, you need multiple words and can’t shorten it.