I guess you'd smell it? And if not does it really matter?

Probably you'd be surprised at how much you poop you consume, both your own and other people's or animal's.

I imagine the bottles are cleaned before refilling.

Everything should be sterilized by the bottler before reusing, but I'm guessing that any bottle to suffer that destiny would be discarded either by the store owner, the pick up crew, or the bottling facility

It's pretty similar in my country

Plastic and glass is ground up

Does it matter? You need to sterilize it anyway, because of the other million environmental factors.

Knowing the Germans, it's a law.