OK,
Lots of pool stores sell liquid chlorine (same as bleach only usually 12.5% solution) in 5 gallon blue drums ("carboys"). The drums can be square or round, but square is better. You put a deposit on the drum the first time you buy it, then return the drum when it's empty and don't pay another deposit. Lots of pool stores use the square drums--at least 3 in my area --and they are all the same so you can use them anywhere. But only one uses the round ones.

But if you get a carboy, it's far easier if you buy the spigot that goes on them. They are about $4. and worth every nickel!

The only thing is that 12.5% breaks down far faster than 6% so unless you dilute it down, it will break down, unless kept cool and out of the sun.

Still, you can test it by add one ml of Liquid chlorine to 10 liters of plain water. (one ml can be gotten from a used up kid's medicine dropper for tylenol or lil' noses. 10 liters is simply 5 2-liter soda bottles worth).

Whatever your reading is will be the concentration. So if you read 10ppm, your concentration is 10%