When common devices can not reach far sufficient or work quickly sufficient, Mighty Probe is the device for the job

https://blast-wiki.win/index.php/Septic_Probe_Rod_Basics:_Just_How_to_Find_a_Septic_System_Efficiently

When ordinary tools can not get to much enough or function quickly enough, Mighty Probe is the tool for the task, giving you the depth, rate, and control needed to get it done.