things can work well one day and break the next.i think you did all you could do. i'm not sure if there is a pressure test for sewer systems or not. i know the last house i bought, there was 99.99% saturation on one of the walls. i was sure that there was a leak in the pipe behind the wall. i called out a leak specialist and he said that he could detect even the smallest of small holes in a pipe. the saturation ended up being from the window sill being sloped and the water ran into the wall. easy enough fix.the $75 charge to have the leak specialist eased my mind, but in your case, if there wasn't even a faint leak or crack, i don't think you would have had anyway of knowing beforehand.

He took 2 hours, took almost 400 pictures including thermal, and water detection. 

I know a general home inspection will not be able to detect such issues that could be behind the walls.

You and Rick are correct that it's a pos property and not worth the time, but my curiosity and love of real estate detective work is having a hard time dropping it.

Because I tested out the tools and found each time big issues, most of the time due to the quality of the initial data, that automated tools don't detect, but an experienced investor does.

I'm looking at a FSBO mobile home which has a For Sale sign in the window but no phone number on the sign. Also I noticed a tag from the Post Office attached to the front door stating there is a certified letter which...

They are master detectives and problem solvers.

Good luck I already detected the issue when we try to purchase, I can't share the detail though.

@Tokes Odumosu  a private detective may turn up relatives you don't know about. 

Mike bought over 100 properties while being a full time police detective in Louisville, Ky.