Our employer was happy to give us a 300 gal chemical tote. These things are ubiquitous. Plastic tank inside a metal cage. Nice drain valve on bottom.
The chem suppliers usually want the totes back, but what really happens is the totes start to build up at the end-user's facility and they'll usually decide to get rid of them at some point.
We picked thru the totes and found one that had held a relatively innocuous chemical (polymer flocculant), then flushed it out for a few hours and took it home.
Might be worth checking around. Ask a few friends who work in industrial type occupations. Maybe the local water treatment facility would have floc totes.