Re: Time for a pro???
I'd say go rent yourself a 100' power snake. It has a larger cutting head and longer reach which should be able to remove the blockage completely. If that doesn't work, then think about hiring a pro with a camera.
While you're clearing the clog, pay attention to how deep you have to go to get to it, this will give you a clue of where you'll need to break the slab should you decide you need to do something more aggressive.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!