Hypochlorite bleach will break down biomat and sludge so if the drainfield is locked due to this, it might work. But if the field is locked due to reminerialization of limestone or caliche, it does nothing. Sodium hypochlorite can sodium lock clays causing a mineral gel so only calcium hypochlorite which is safer. Use tablets in tge distribution box, not the septic tank.. It will reduce beneficial microbes so dont use often.