Locating drain pipes in basement

How does one determine where the metal drain pipes are laid under a concrete floor? I am not aware of anything other than a metal detector.

There is equipment that is made for locating pluming, One type has a transmitter normally called a sondes, and is attached to a snake or a camera and inserted in to the pipe, (and some cameras I believe have it built in) that then a locator can be used to determine where it is and how deep it is.

I have never used one only read about them and there use.

Some plumbers have them. Who knows may be a rental would to.
This is one type and brand. There are others
http://www.ridgid.com/Tools/NaviTrack/index.htm

pipes

Metal pipes can have a tone introduced to them which can be detected by a receiver. One problem is that if other metal pipes are connected to it somewhere, the sound can be transferred to them also making an accurate tracing difficult or impossible.

When you locate them, what are you going to do? Or why do you want to find them?