Disinfection of the waste water is a necessary evil for OBDs. Waste water that looks clean enough to drink ISN'T, even the best sandfilters or mechanical treatment systems do not eliminate the pathogens in the waste water. Disinfection is usually accomplished by chlorine, although a few OBDs use ultra-violet radiation. These tablets have been distributed by service contractors or chlorinator manufacturers historically. Recently, a number of you have noted it is increasingly difficult to find the these standard chlorine tablets and are not sure how to use them when you get them.
Moisture causes the unused chlorine to swell, clump and generally become useless.
Check to ensure the screens are still in the bottom of the tubes. Large chlorine tablets or sticks used for pool water disinfection can be substituted for the standard tablets. Sticks and tablets are available anywhere they sell pool supplies. Check the chlorine level at least once a month. Always handle chlorine of any kind very carefully, store in a cool dry place away from children.