Plastic isn't necessarily perfect, it can e.g. be affected by substances like acids. I'd be incredibly surprised if there wasn't a material difference between a "virgin" piss bottle and a 10-year one.
If those material differences cause a layer of piss to stick to the plastic which isn't easily cleanable and dissolves into food over time, they're gonna care about them.
there's a handy round section of a cylinder made out of a silvery metal, with embossed motives on both sides, that carry this exact value, you can use it to trade for an item deemed similarly priced