Bio-Clean (Terry sells it) has been helpful in my overworked system, but a healthy septic tank that is not abused is typically self-sustaining. Take an annual look to see whether any crust is building up on top of the liquid inside and have the tank pump and cleaned if any crust builds to more than a couple of inches.
More important, in my own opinion, is to be sure you have a filter at the outlet end of your tank to protect your drain field. Prophylactics float and do not dissolve, and I discovered a *lot* of somebody else's floating on out into my drain field during my first inspection right after my wife and I bought this place.
I make it clear to anyone and everyone who *ever* uses a toilet here in my home that *nothing* other than single-ply tissue is to ever be flushed until *after* it has been eaten, but I still catch all kinds of stuff (including chewing gum swallowed by my grandchildren) in my outlet filter.