I have to wonder where some people get these ideas....????..... I have a septic system, have had for 40 years, and I use bleach with whites, once a week or so. We have always had a garbage disposal, too, NO PROBLEMS. My parents did the same and so do my brothers, who live on this same farm, no problems. We have ours pumped out every three years, as recommended, but I know my parents did not do that.
I was told by a plumber that a garbage disposal is a GOOD thing for septic tanks because it adds bacteria to the tank, which helps it "work". Makes sense to me.
I know people who did not have a garbage disposal because they "heard" that it was bad for their septic tank. My family has a combined 100 plus years experience that says otherwise.