I've cleaned a lot of plastic totes and barrels, and in my opinion the best thing to do after you've cleaned it is to ask yourself "would I use this for drinking water for my family?" If the answer is yes, you're probably good to go. If not, I wouldn't put fish in it.
If you decide to try it, I recommend a powdered brewers wash for cleaning. Some types of plastics are porous, and are difficult to clean.
