How to use a sewer camera on a cloged drain?

[bill78]

hi guys im a plumber and have always been taught that the line needs to be cleared first before i can use a sewer camera to pinpoint the problem area. I remember we would use a pump truck to vac out all the sewage and then run the sewer camera (not always effective). But I would like to know if anyone has any tips on how to locate the problem area under a shopping mall slab on a drain I cannot clear. I know about the listening for the snake spinning at the problem area. How can I use a sewer camera in a line full of sewage?

 

[hj]

If you have a good camera and locator, push the camera till it stops then use the locator to find where it is.