Folklore: The folklore of septic systems could probably fill a small book. Like most folklore, the stories reflect elements of truth, ignorance, and humor. Hopefully, this information will help to keep your septic system working well for many years.
Bacteria: The bacteria in the septic tank eat and digest most of the waste. But there's always some waste that doesn't even appeal to these critters. As a result, the health department recommends pumping out the tank every three to five years. (The PCMA's Septic Management Program requires pumping out the tank every three years.) This will remove excess sludge that has accumulated.
Common Myths - Dead Cats and a Pound of Yeast: Theories abound about the best way to start up a new septic system. Most theories deal with "seeding" the septic tank to get good bacterial growth started. Advice has ranged from flushing a pound of yeast into the system, to seeding the septic tank with manure, all the way to placing a dead cat in the septic tank. However, no special seeding is necessary to get them started. The simple act of using the system will provide all the bacteria necessary to make the system function well. Yeast, manure, and especially dead cats, will not help develop the colony of bacteria in the tank any faster.
Additives for Old Systems: Septic system folklore doesn't stop with seeding a new system. Many products are sold that claim to make old systems like new. Other products claim to eliminate the need to pump out the tank. These products usually contain yeast, bacteria, enzymes, or chemical degreasers. So far, no additive has been proven effective in a controlled scientific study.
Why Additives Don't Work: Some of the solids in the tank are sand, grit, bits of plastic, and similar materials. No enzyme or bacteria can digest these. Other organic solids are not very digestible. Hence, they accumulate. Bacteria that are added must compete with bacteria that have adapted to living in your septic tank. These adapted bacteria have the home-field advantage. The newly added organisms can't compete and become dinner for the resident organisms. Enzymes, on the other hand, are not living and cannot reproduce. Whatever is added to the tank is all that will ever be there. Most septics are 1,000 gallons or larger and the quantity of enzymes added is too low to be helpful. In short, adding enzymes or bacteria usually won't cause a problem (except for two types - see below), but they won't help either. The solution is simple. Have your tank pumped at regular intervals. The solution is safe, easy, and much cheaper than buying those septic tank additives.
The PA DEP, when asked about septic additives, replied that the Department has determined that there is no scientific basis for the beneficial claims made regarding septic tank additives. On numerous occasions, the DEP has asked product distributors and manufacturers for data supporting their claims, but has never received a response. The PA DEP regulations do not control additives. There is also no data to show that the additives do any harm to systems except for two types: Hydrogen Peroxide additives and Surfactants, which break down grease, but cause these materials to blow over into the soil.