55 gallon barrel with a good lid. I cleaned my barrel out either this year or last year for the first time in a couple of years. It was very clean and not even worth doing. I only have a TDS meter in line so I didn't check, but any tds creep would be something I put in, there was no bacterial slime or anything. I drilled a hole in it and use a uniseal since it's round instead of a bulkhead. There is a bit of pvc with a ball valve.
They are readily available most places used for cheap, just make sure whatever was in it first was food or food grade. Mine had tomato juice in them, and yes they did smell for a while, but I put bleach in them and sun dried them and eventually the smell went away. I've been using the same ones for 6 years or so.