How to tell if your cast iron septic tank pipe has failed

Send a sewer camera down it or dig it up

There are at least 2 pipes to check and the first one is the only one you can check with a camera. The pipe between your home and tank can be scoped with a camera. A good contractor can also tell by "feel" with his rodder. The next pipe connects the tank with a distribution box and you can't see it with a camera or a rodder, got to dig it up. Tell us why you suspect a problem, when was your tank last opened and pumped, is it full now?