Sludge is the settled solids layer that accumulates in the bottom of a septic tank.
Why it matters
If solids accumulate excessively, they can migrate out of the tank and contribute to drainfield problems. A service professional can inspect sludge and scum levels.
The maintenance implication
Pumping physically removes accumulated material. Think of an additive claim as equivalent to that service.
Useful next reads: maintenance guide · warning signs · septic additives evidence