I have my tank pumped and inspected every three years. He marks the spot alwasy. The last time the guy was here, he found that that the line to the house had buckled and cracked and was on its last legs.
He brought in a little back hoe and laid a more solid and durable new pipe with some vents for the sewer gas. I think the new system will outlive me.
I also have my chimney swept every few years; it is cheaper to do regular maintenance than have a hideous domestic emergency similar to that which JP described.