The sludge judge is tool for evaluating the sludge and scum in a septic tank. It consists of a clear plastic tube about 1.5 inches in diameter and has a remotely operated shut of valve on the lower end. The sludge judge is lowered into the tank with the vlave open. When the tool touches the bottom the valve is closed and a "core" of the septic tank effluent is removed for viewing. The photo on the left shows a brand new sludge judge getting dunked for the first time.
You have to look closely but the left photo shows a tank that's been in use about 2 years. There's about eight inches of accumulated sludge at the bottom of the tank and about 4-5 inches of floating scum on the top. This tank doesn't need to be pumped.
The photo on the right shows a sample with sludge from top to bottom. There is no clear zone. Even though the tank had been in use just over a year, it was time to pump the tank. Garbage grinders are a common cause of this sort of problem.