Does my house have a cleanout?

My house was built in 1955 in New Carlisle, OH. It is a 3 bedroom ranch with all of the plumbing in one location. I can follow the stack to behind my kitchen sink which is also roughly behind my toilet and then it goes into the ground. I've dug a little bit and can't find the drain. and worse still, I can not find a cleanout. When were the codes requiring them introduced? Is it possible that I don't have one? I'm sure I just haven't dug deep enough to hit the pipe but wouldn't I have hit the cleanout already even if it was buried? Any ideas?