This type of drain odor typically indicates that you have a blocked branch line or vent. You'll need to remove the clog, either by hiring a professional to do it or trying a hand auger. Liquid drain cleaners don't work on long horizontal pipe sections because the cleaners settle on the bottom of the pipe and clean only the lower part of the pipe. If your pipes are made of steel, you should avoid acid-based drain cleaners. Acid eats through the zinc coating on galvanized piping, clearing the way for corrosion. Similarly, cast iron pipe has a tar coating on the inside – and acid will eat through the coating, leaving the iron exposed to the water and corrosion. Even if your pipes are plastic, many of the city mains and services into homes are cast iron.