Medium – Some Fill Dirt
For the property pictured below, I knew where the drain line exited the house and I only needed to probe the yard. The yard had no fill dirt except over the septic tank. So, I only needed to probe the topsoil to look for ground which was easily penetrated by the probing rod. The tank was easy to find within the small section of ground which was easily penetrated by the probing rod.
Hard – Never Pumped and Any Fill Dirt Settled for roughly 60 years
For the property pictured below, the entire backyard was hard clay with granite. The dirt over the tank was the hardest dirt seen by one of our team members [a master plumber with over 40 years of experience]. The ground could not be reliably penetrated more than 2 inches with the probing rod more than 2 feet away from the foundation of the house.
I was able to locate the drain line exiting the house and into the yard [this was not a straight line from the exit seen under the house]. Once the drain line was marked, we received permission from the homeowner to excavate the yard in order to locate the septic tank. We followed the drain line out and located the septic tank on our first deep hole. This would not have been possible without a deep hole, and this process was impractical with hand tools. The post hole digger would have kept us at the property all day. Luckily our excavator made short work of the location process.