How to check or fix leak in concrete drain pipe?

We have a 6" concrete drain pipe running 10 feet along a flat section and then 25 feet down a hillside to the lower part of the back yard. Near where it starts there is an access hole T. About 10 feet away from this access hole (where the hill starts) the concrete of the floor is caving in a few inches. This is also close to the corner of two retaining walls. There was a beehive inside that we had to have professionally sealed up, so apparently there is a cavity down there. Now, what I am suspecting is that maybe there is a break in this 6" concrete drain pipe which no one has ever noticed because it's completely underground, and this break could be causing the soil erosion (hopefully not, hopefully it's just soil settling). I would like to check it. I was thinking of getting one of those inspection cameras with a camera on a long snake, but not sure if it would be long enough and pricey to use it one time (I wonder if these are available for rent). If I find a broken section of the concrete pipe, how could I fix it? Some kind of plastic liner, or pour some kind of epoxy down the pipe through the access hole?
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p.s. somebody might suggest to dig down and check out the pipe, but that would not be possible due to having to break up concrete ground above a precarious location near retaining walls and a slope; a huge digging job could cause more damage than good by displacing soil in a fragile section, especially if the pipe is not even broken.
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