answer:Yes, it is bad to do so. Remember that septic tanks work by having cells take the incoming kitchen and bathroom waste and converting that into, well, waste. In other words, the microbes are converting the by eating it. Bleach (and other chemicals) kills the microbes. No microbes, and the septic stops decomposing the waste, and it backs up, and you get it pumped more frequently. Now, a teaspoon of bleach isn’t going to matter. But a significant amount frequently—bad news. DOn’t do it. Especially straight bleach. Dilute it with a TON of water. (Septic in my back yard)