I kind of bought too much Caustic Soda from a chemical supplier in bulk as it was the only place around that had close to 100% and I don't need it all.
Use it for soap or for essential oil extracts, maybe you have a real bad drain.... idk
There's ~20kg available.
$15/kg + what ever postage is, or pickup Northern-Western Suburbs of Melbourne
or the whole 20kg for $100 (but you'd have to pick up)