Originally Posted by Cheesesteak
The supply pipes and waste pipes are entirely separate systems.
CORRECTION.The supply pipes and waste pipes are SUPPOSED TO BE entirely separate systems.
You would be surprised what plumbing inspectors find!
Most of the time a compressed gas drain clog buster will do it's job with mo harm done. The exception is a disaster!
Get a hydraulic 'DraIn King," hook it to a garden hose and turn on the water slowly. It will clear any clog except poured concrete. Disconnect immediately as it is connected by what is called a cross connection to an usafe source in most cases.