How to Create Cavity/Hole in the Ground

The white uPVC pipe is supposed to pass through the Concrete Drain so that all the effluent from the Septic tank flows into the drain. But this pipe cracked at the joint and after many years, the effluent eroded the soil surrounding the pipe, resulting a huge hole behind the drain. 
Such is the power of leaked water, often creates dangerous holes/cavities in the ground.