You need a special pump if you have a drinking water softening system or a condensing system (heating system) in your household. The waste water from these two systems contains corrosive or highly saline substances.
Due to the processing of higher-quality material, the special pumps are considerably more expensive.
These attack, for example, the impeller of the wastewater pump. In a special pump, the impeller is made of stainless steel and is therefore resistant. However, you should check carefully whether you need a special pump.