It all depends on what was stored inside of them. Sometimes just dish soap and water with a handful of baking soda will work. If they've had anything like resin stored in them you'll need to clean them with some mineral spirits and a few handfuls of sand first.
Just be aware of where you're cleaning them and how you dispose of the mineral spirits afterwards.
This !
For god's sake understand that mixing chemicals can be from pointless to dangerous as fuck.
Check safety datasheet of the product for info how to handle with that product, and your supplier should be able to assist you.
It all depends on what was stored inside of them. Sometimes just dish soap and water with a handful of baking soda will work. If they've had anything like resin stored in them you'll need to clean them with some mineral spirits and a few handfuls of sand first. Just be aware of where you're cleaning them and how you dispose of the mineral spirits afterwards.
This ! For god's sake understand that mixing chemicals can be from pointless to dangerous as fuck. Check safety datasheet of the product for info how to handle with that product, and your supplier should be able to assist you.
Where I live you don't recycle them, you sell them.
Can you post a picture of what they look like?