Chlorine... pool stores generally will carry 10-12.5% jugs of it if you want to minimize your number of containers to recycle.
Some big box hardware type stores carry them as well. Here, we have Menards and Fleet Farm that carry it seasonally. Some Home Depot stores carry liquid bleach/chlorine of high strength. Some Wal-Mart stores do as well, but not many. If there are no readily available sources of high % bleach, you can go with the higher concentration household bleach from Wal-Mart or other retailer. Look for good prices on the 8.25% bleach, preferably a place that sells alot of it so it's fresh. The disadvantage of liquid bleach is that it degrades over time. The fresher the better. Most bottles will have a date or "decodable" date code to tell you how old it is. Stay away from low concentration, old stock "dollar store" bleach. Lower household bleach concentrations means more containers to lug/recycle but it doesn't degrade from original concentration quite as fast.
Some big box hardware type stores carry them as well. Here, we have Menards and Fleet Farm that carry it seasonally. Some Home Depot stores carry liquid bleach/chlorine of high strength. Some Wal-Mart stores do as well, but not many. If there are no readily available sources of high % bleach, you can go with the higher concentration household bleach from Wal-Mart or other retailer. Look for good prices on the 8.25% bleach, preferably a place that sells alot of it so it's fresh. The disadvantage of liquid bleach is that it degrades over time. The fresher the better. Most bottles will have a date or "decodable" date code to tell you how old it is. Stay away from low concentration, old stock "dollar store" bleach. Lower household bleach concentrations means more containers to lug/recycle but it doesn't degrade from original concentration quite as fast.