The oil from new metal products is usually placed there by the manufacturer to prevent rust before use and extend shelf life. No one will buy a rusty bucket.That 'oil' might be from the manufacturing process and should dissipate pretty quickly.
Who knows what plastics might leaching into any consumables.
If you drilled a couple holes at the bottom of a gallon glass jar and had a tight fitting lid, you could put that inside a deep glass dish so it would work like a normal waterer. There's your glass waterer! Who's gonna make it first?you should manufacture a glass waterer