To add to what BobB already said, you can use almost anything to 'shove' up that pipe (assuming you have clear access to it) to see how far 'it' will go until it stops. I've used a garden hose a time or 2 because it's flexible, yet stiff enough, to be shoved up the pipe. Do understand that when you 'mark' the hose (to indicate how far into the pipe it went), and actually measure the 'distance' (after pulling it out), you may have to dig a few feet on BOTH sides of that 'location' outside the wall. The reason is because the hose can 'bend' and/or 'bind' enough over a large distance to give you a somewhat 'false' measurement.
You may be able to even use a Plumbing Snake to shove up there. The only problem is it may get 'hung' on just about anything. Oh, that reminds me - Wrap the tip of whatever you decide to shove up there so the tip DOESN'T get hung up.