Sometimes you need dig up your sewer line, but if you have just moved onto the property or have never had to do anything with the sewer, chances are you don't know where to dig. It is reasonably simple to locate where the sewer line leaves the house, but where does it go to connect with the city's line? There are ways to find these lines without digging up your entire yard. Some are new and some have been around for centuries.
Contact a city maintenance person and ask. In small towns there is usually one man who can tell you where the sewer lines are located.
Ask at city hall if you live in a larger town or city. A sewer department should have an infrastructure map that you can examine. This is shows at least three things you will need to know: how far the city main is from your property, where it is located and the depth of the lateral service connection.
Contact a plumber. Some have small flushable cameras. Once the camera is flushed down your drain, it can show you the location of the line and tell you the depth of the pipe. A plumber may also have radar that penetrates the ground to show the sewer pipes.
Witch or dowse for the sewer line. This is an ancient way of finding water sources. Get two lengths of heavy wire. You can use welding rods or coat hangers. Bend one end of each rod at a 90 degree angle. The rod will resemble an L shape. Hold the short bent end or handle of the rods in each hand. The long ends will point out in front of you. Walk slowly around your property where you believe the sewer line is and wait for the rods to cross. When they cross, making an X, you will have found your sewer lines. You can also use willow twigs; do not bend the twigs at an angle, though.
Climb up to your roof sewer vent. Line up the sewer cover with the outside clean-out line. Once you line up the two, aim across in a straight line and that will tell you where the sewer is located.