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Just realized that probably not everybody knows this: when sorting plastic waste, and you're not sure whether something can go in the plastic waste... if in doubt, put it in mixed waste!
The potential consequences of mixed waste in plastic collection are much worse (can make an entire truckload of plastic useless, depending on local collection process) than the potential consequences of plastic in mixed waste (one piece of plastic wasted).
(If your local waste collection program has different instructions for "when in doubt", then follow those; but almost no collection agency seems to specify this, for whatever reason)