That mysterious sound coming from the sink after the toilet is flushed isn't a sewer gremlin. It's a sign that there might be the beginning of a problem with the sewer connection in your bathroom. Caught early enough, this problem can be taken care of fairly simply. But don't let the gurgling continue for too long, or there may be expensive sewer repairs on the way.
The plumbing for all the fixtures in a house -- sinks, bathtubs, showers and toilets -- all meet together at the main sewer pipe called the sewer main. This is usually buried in the front or side yard of the dwelling and runs out into the street where it meets the municipal sewer lines. In a remote location, such as in the country, the sewer main will usually run to a septic tank.
Although it might not seem obvious, the sink in a bathroom and the toilet are usually connected. The smaller pipes from the sink will run inside the wall or beneath the floor and meet up with the larger pipe from the toilet, which is called a closet flange. Both the sink and the closet flange will have an additional pipe leading up from a tee connection to a vent pipe on the roof. This allows sewer gases to escape without getting built up in the pipes. A gurgling sound that comes from the sink when you flush the toilet is usually the result of a blockage somewhere in the closet flange or main line.
Unclogging the Toilet
The easiest place to start when investigating a gurgling sound is to see if there is a clog in the closet flange. A tool called a closet auger is used to probe through the toilet pipe and break up any clogs present. The auger consists of a long, snakelike chain that is fed into the toilet. One end of the chain has a handle on it, the other a small spring or hook. As the auger is fed into the toilet, the handle is turned, helping to break up anything in the way.
Unclogging the Main
If the gurgling isn't cleared up by unclogging the toilet, the problem could lie with the sewer main. These problems are more tricky to clear, but the general procedure is the same. Most sewer mains will have what is called a "clean-out plug" located along the line somewhere. Once the cap on the plug is removed, the line can be augered out. For big jobs like clearing a sewer main, call a professional plumber, who will use an electric auger.