Is there a way to detect buried plastic piping.....Yes
If you were to snake your plastic waterline and use a line detector "wan" to detect your outside lines. You would have to hook up the transmitter to the snake (used in plumping) and you will be able to detect them. Be sure to shut main tap outside first then snake through your one inch service. Another way is to use GPR....Ground pentrating Radar...expensive but useful.Use GPR keywords on the internet to find more information.
Myself have been in the same situation and remove old direct buired waterline with special 1.250 Polyproplene waterline that has a locator wire extruded in. We remove the old service in a matter of minutes and restore service in about two hours.