You should not be able to see the flow of water from the roof if the bladder is headed down the drain line. The bladder should puff up, and the water should be flowing down. So nothing to see from above. If you are only putting the drain bladder into the trap adapter, that will not be able to pressurize the clog, and it will not be able to direct the vibrating stream to the clog. If you are unable to turn the corner down, how about inserting the drain bladder through the roof vent, and continue it down past the sanitary tee.
I used the bladder at the pipes entrance into the wall, not in trap(not easy to do with elbow so close). Only water running when I checked the roof vent was in the drain that is having issues.