Best to get new... you never know what had already been stored in those trash cans if purchasing used.
I thought of that after I posted, so I asked. He said they were used to ship Apple Juice. On one hand, I think I should be able to clean them out pretty well. It's not like they had pickles in them...
I had actually planned to buy three containers anyway, at ~$40 each. One for fresh RODI water, one for mixing SW, and one for waste water from the RODI which I plan to use to water plants, etc.
So, I'll buy two (I can only fit two in my car anyway). If I can get them clean enough, I'll buy two more, and have two waste water storage containers instead of one, and I save ~$60. If I can't get them clean enough, I'll buy two Brute cans for RODI and SW mixing and use the two barrels for RODI waste water, and I save ~$10. And, either way, I win with more RODI Waste water storage capacity and less expense.