Bathroom backing up at main access point

[ajmcgraw]

Situation: The bathroom was recently getting clogged, and plunging/snaking with a small snake from inside did nothing. There is a main access pipe outside the bathroom that goes out to a public manhole that is far out in our backyard (shared with neighbors). So I opened the lid off the outside access pipe (pictured), and all the backup came up outside (toilet can flush when this is open). So I figured the main pipe must be clogged.


What I tried: I rented a 100 ft snake and snaked the main from this access pipe all the way to the manhole (I lifted the cover on the manhole and verified that the snake reached). I did it twice, one with a cutting head and again with a coil head. So it's gotta be mostly clear... Problem is the bathroom still clogs, and if I open the access pipe, it still rushes up and out of the access pipe.

Question: Why is it still backing up? The snake cutting head is huge, so the pipe is definitely clear all the way to the manhole. Why doesn't water want to go there? Does this have something to do with a difference in water pressure somewhere? I simply don't understand what is going on. How can this be fixed?

Thanks!

 

[Silentrunning]

Is it possible that over time some of the pipe has settled and is running uphill from the access hole to the manhole? Don’t trust your eyes on this. Take two pieces of wood and a string to check the pipe level.