Which type of discharge is not permitted for washing machines in a plumbing system?

In plumbing systems, the type of discharge that is not permitted for washing machines is a direct discharge. A direct discharge occurs when wastewater from appliances, such as washing machines, is released straight into the drainage system without any form of protection or separation. This type of discharge poses potential risks, including contamination and backflow into the washing machine, leading to health hazards and violations of plumbing codes.

In contrast, indirect discharge methods, such as discharging waste through an air gap or an air break, provide protection against backflow and ensure that the wastewater is safely contained before entering the drainage system. Discharge via a pump is acceptable as long as it is designed to handle wastewater effectively and meets all plumbing code standards. Thus, the prohibition of direct discharge is critical for maintaining sanitary conditions and preventing pollutants from entering the potable water supply.