A BARRELL? How much are you extracting?!
Chemicals can leach from plastic, and there will be softening chemicals to worry about as well as the blue colour. I don't know about whether or not HDPE will stay solid when filled with naphtha, but personally I avoid plastic entirely anyway because of the potential health risks. It is at least safer and more environmental to use glass or ceramic.
Dreamer tells me he uses a large ceramic mixing bowl. He remembers that the Invader Zim mescaline teks uses glass demijohns usually used for beer/winemaking (or whatever the larger versions are called as I think demijohn refers to the smaller size). These look great because you can put the plug in and roll them instead of having to go through the tedium of stirring all the time. He wants one of those.
People give them away for free on Ebay because some are enormous and they don't want to have to take them to the dump themselves.
Everything I write is fictional roleplay. Obviously! End tribal genocide: www.survival-international.org Quick petitions for meaningful change: www.avaaz.org/en/
End prohibition: www.leap.cc www.tdpf.org.uk And "Feeling Good" by David D.Burns MD is a very useful book.