Powdered detergents contain surfactants and phosphates which can harm your septic tank. "If it's a powder ... Instead, try an enzyme-based cleaner or, if you're dealing with a more severe septic ...

A septic system isn’t much good if it’s clogged, and once it is clogged, it’ll cost a fair amount to pump it—but using a septic tank treatment every so often can help prevent this.