Had an in law that washed almost every load of clothes with bleach, cleaned toilets by pouring bleach in them. I think she used bleach for everything and it did cause them septic system problems. Beneficial bacteria that break down the waste are killed by too much bleach. Drop-ins in the toilet aren't enough to do it, but overuse of bleach is.
We too have had the seals of toilets fail because of drop ins.