You will be listening and feeling for the layering in the pits. At least where I dig, people either had wood ash or coal ash to toss into the privy to keep the smells down. This action would cause the layering in the pit. The surrounding ground feel harder, sandier like sandpaper as you push the rod down. Look at the tip of the probe to see what you bring back up from down below. Look for small dirty soil samples, darker than the surrounding dirt. Listen for the unmistakable sounds of rocks, bricks and finally glass. Once you find a pit, probe to the sides and feel the difference. You wont forget it. Then the trick is to call what age the pit is before you dig it. I would say we are 75% good on the age before we dig. You will get used to it if you probe enough and dig everything at first. Goodluck jgas