” Then to each gallon add a few drops of Clorox and let it stand over night. “
Household bleach in the common plastic container has a limited shelf-life - the chlorine molecules come out of suspension and are tiny enough to pass through the pores in the plastic...
If you’re storing bleach long-term for survival purposes, transfer it to canning jars, or other tight-sealing glass containers.... (Metal, not so much - chlorine is extremely active, and will corrode metal...)
Better yet is Calcium Hypochlorite easy to store and a little goes a long way: