> It's relatively hard to sanitize PET because tiny defects hold contaminants really well. https://en.wikipedia.org/wiki/Polyethylene_terephthalate#PET.... Also I would guess that the defects add up over time and you'd need a way to test each bottle's integrity before shipping it out again.

From your sibling comment. Just reposting since you might not other see it and it seems to address your question. Well, assuming these bottles are made from the same sort of plastic.