I am trying to find the sewer drain pipe or clean out if there is one. Plumber says it will cost a lot less to install a clean out if I can find the drain pipe. The house was built in the late 70's on a cement slab. Are there any guidelines as to where I should be digging, or how deep the pipe would be. I have been digging across the front of the house, down to about 12 inches, but have only found water lines from an old sprinkler system. I have started digging near the outside water faucet which is in line with the toilet in the main bathroom. Any suggestions would be greatly appreciated.
Thanks
Barbara

A "smart plumber" ought to be able to find it. If it's cast iron, then locator systems can be used. If PVC, the toilet can be lifted and a snake put down the toilet pipe. Then this can be located with electronic detectors.

Digging is like looking for a bone. 12" is probably way to shallow.

In my area, exterior main clean out is usually within 24" of foundation in front of your house. There, sewer pipe with plug extends to the surface. However, many times it slightly buried.

As KISS correctly stated, any experienced plumber should be able to guess where the clean out is by familiarizing himself with your house layout, bathroom position and vents on the roof. Clean out can also be located by Pipe Locator. However, locating using Pipe Locator requires expensive equipment and will carry some extra cost.