Most all drain openers have some sort of Acid in them. Septic tanks use little microbacterials to decompose waste. Once the waste is liquefied it often travels into a leach field and is released into the soil. The acid in the drain openers will kill the microbacterials in the septic tank and cause the waste decomposition process to take longer. Normally using drain opener every year or few years will not harm your septic tank. If you use drain opener on a regular basis then it could harm your tank. Did you know? … every time you use your washing machine the bleach and detergents kill off microbacterials.