Add 1-2 bottles a year for preventative maintenance depending on the usage of the system, the age, and the number of people in the household. If the pit is operating efficiently, they should be essentially free of standing water. They should absorb as much water each day as is added. This, however, rarely happens especially in an older system.
If you have access to the distribution box or directly to the laterals, add the bottle directly into the distribution box or divide equally among the laterals. Add to the distribution box and distribute with a hose until it is all flushed into the drainfield.
Cesspools are similar to seepage pits except there is no septic tank. Cesspools function as both the septic tank and water absorption field. They are the hardest systems to treat. Cesspools should be pumped and cleaned about once a year to prolong their life. After they are pumped, the treatment is the same as for a seepage pit.
A seepage pit is a pit with a septic tank before the pit. These pits may be constructed in many ways. The goal of treating a seepage pit is to treat the bottom so that it absorbs water better. The sidewalls account for only a small percentage of the water absorbed. It is more important to treat the bottom and let the sidewalls take care of themselves.
The most effective way to treat the pit is to first pump the water and then backwash to break up the bottom. If during this process water from the sorrunding area refills the pit, remove this water and leave about 100 gallons in the pit. Add two bottles of Septic-Scrub and another two the next day. You may have to add water the second day if the water has all drained out of the system. Additional treatment may be necessary.
After a seepage pit is treated, its almost certain that it will start to fill up again as the bottom clogs again. If you have access to the pit, you can hang something like a fishing bobber so that it will float when the water level reaches about 25% full. When it floats, add two bottles of Septic-Scrub. There is no way to predict when the water level will reach this level. This technique will help prolong the time between pumpings.