Document Type

Technical Report

Publication Date



Septic tanks, Bacteria, Household chemicals


A laboratory study and a field study were performed to determine the amounts of specific household chemicals required to destroy bacteria populations in individual domestic septic tanks. The particular chemicals evaluated include liquid chlorine bleach, High Test Hypochlorite (HTH), Lysol disinfectant and Drano crystal. The laboratory study was performed to determine the approximate chemical concentrations to destroy the bacteria in the septic tank, and the field study showed the actual effect of the chemicals upon the bacteria in terms of reduction of the number of bacteria in the septic tank as well as the time required for the bacterial population to recover. A liquid bleach concentration of 1.85 ml/l destroyed the bacteria in the septic tanks. This corresponds to 7 liters (1.85 gallons) of liquid bleach in a 3780 liter (1000 gallon) septic tank. After addition of chlorine bleach, and within approximately 30 hours of normal septic system usage, the bacterial population had recovered to its original concentration. A Lysol concentration of 5.0 ml/l destroyed the bacteria in the domestic tanks. This corresponds to 19 liters (5.0 gallons) of Lysol in a 3780 (1000 gallon) septic tank. Following the addition of Lysol, the bacteria population recovered to its original concentration within approximately 60 hours (2.5 days). A Drano concentration of 3.0 mg/l destroys the bacteria in a septic tank. This corresponds to 11.3 grams (0.4 ounces) in a 3780 liter (1000 gallon) septic tank. The bacterial population recovers to its original concentration within 48 hours following the addition of the Drano.

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