I have always heard that saying.  Pretty much means that China is on the exact opposite side of the earth from us.   Well I found that is completely false with the help of this quick and easy webpage.   Finding the exact opposite side of the world from where you are actually has a name, it's called looking for the antipodal point on the globe.

This website is very utilitarian, but I spent about 30 min on there seeing where you would end up on the opposite side of the planet from random locations.  Seems like pretty much the entire US is exactly opposite the Indian Ocean.

From East Texas, we would be right smack dab in the middle of the Indian Ocean.  The closest thing we have to a country that is on the opposite side of the globe is Australia. I wonder why they didn't think of Australia as the place to dig to when the saying started? The toilets flush backwards there so it was the clear choice!