Get a call Friday afternoon, hour before Shabbat. Drains not working on a renovation we recently completed. Told the contractor the clog is probably originating outside, not my lines as they are all new and checked. I get there Saturday night and clear the line.
Get a call the following Friday at 11:00. Clogged again. Get there at noon. Work until 2:00. Pull out a lot of baby wipes but this time no success in clearing the clog. I tell the contractor there must be a hidden manhole or a bend with something gone awry. I'm leaning towards the former. Tell him I'll be back Sunday morning first thing with my sewer camera, locator and excavation equipment.
Send in the video camera until I hit the spot where I had been getting stuck. Can't see anything as the line is full of water, but that doesn't matter. Activate the sonde, get out my locator and start walking around the patio. I soon find the location where my sewer camera head is located. I start digging, opening up the Jerusalem stone patio, breaking concrete and soon find the pipe. Little more digging and find a covered manhole cover. Years ago a hotel next door renovated the area. The workers ruined the manhole, rocks fell inside (cause of the clog), and they covered right over the access cover! Surprisingly enough this happens more frequently than one would think.
I clear out the mess, open up the hole more, get a new cover and ring, raise up the sides of the manhole, install new Jerusalem stone -- and voila! Done like a pro.