>first time dealing with a moldy bidon
>forgot to unscrew one, now it is starting to smell like a puddle
>put in some of the sodium metabisulfite i still have
>pour in some water, shake, let sit
>pour out after a while, allow all the rest of the stuff evaporate
>whala

I felt like I got sprayed by a sulfur spray after I opened it up to sniff before pouring the solution out, but it works like a charm.