Fill with bourbon, shake well,
place in freezer for 24hrs, this will loosen mold from plastic,
go for a long hike in the sun taking a sip of Icey cold bourbon every few minutes,
the first 200ml will still taste a bit plastic,
but after that you wont notice it anymore and will have a great afternoon.

But please wear a helmet as you may fall over occasionally

If it dosent work, rinse and repeat.