Modern battery chargers have circuitry which prevents them from functioning if they don't detect a battery so you'll need to hook the charger to a battery and then the battery to the tank. The battery doesn't need to be a good battery, Any old battery will work.
For a tank you'll need something long enough, like a 50 gallon plastic drum or if you wanted to build it specifically for barrels, maybe a large plastic pipe with a cap on the bottom would probably be ideal.
The tank I've been using is a 275 gallon IBC, leftover from when I was doing metal prep on automotive projects a couple years back and it was big enough for doors and fenders on the Healeys.
Depending on what all you plan on doing, bigger tanks are better for more capacity. The fact that it takes some time makes it nice to be able to jam a bunch of stuff in there at once and you have more room so there's less worries about accidentally causing a short.
On the other hand a smaller tank would have the advantage of requiring less electrolyte.