for RO water only
for mixing depending how much im making ill use a 5 gallon salt bucket, a rubber maid tub or a 55 gallon drum i have. rubbermaid does make large stock tanks in many different sizes (which people like to convert into sumps due to thier size and durability ) but they come with a nice price tag. im not saying buy from here, but this is so you can get an idea of what im talking about, Rubbermaid Stock Tanks
any food safe container should work great, trash cans to however just pre-rinse them very well as i have read an article of a guys tank leaking and he ran around the corner to the closest store for a few plastic trash cans and quickly put his livestock into the cans without rinsing them. apparently one of the cans had a residue which killed the fish in that can. which makes for a good example of its better to be prepared.