In this video, This Old House plumbing and heating expert Richard Trethewey employs his detective skills to find and clear a stubborn clog.
1. From the roof, slowly feed an inspection camera down the vent stack. Watch the monitor until you see an obstruction.
2. Have someone inside the house flush the toilet while you watch the monitor. If you can't see water running down the stack from the toilet, then you've located the clog.
3. Insert a 12-foot-long electrician's probe down the hole until you hit the clog.
4. Remove the probe and inspect its end for clues. In most cases it'll be a mass of soggy leaves.
5. Next, feed a garden hose into the vent stack. Lower it all the way down to the clog.
6. Turn on the water and then poke at the clog with the hose to flush out the clog.
7. Once the water pressure breaks through the clog, flush the toilet again.
8. If you see water flowing from the toilet down the stack, then you've successfully cleared the clog.