Which method is not acceptable for indirectly venting a waste?

Connecting below the flood rim is not an acceptable method for indirectly venting a waste because it poses a significant risk of backflow and contamination. The flood rim is the highest point that a fixture such as a sink or toilet can fill without overflowing. When a waste connection is made below this level, there is a possibility that wastewater can rise above the connection point, leading to potential surcharges of dirty water into the system. This situation can jeopardize both public health and the sanitary conditions of the plumbing system.

In contrast, discharging into a dry well, utilizing a trap, and using an air gap are recognized practices in plumbing code and help to ensure that waste is adequately vented and that there are safeguards against backflow or contamination. Discharging into a dry well keeps waste away from surface water. Traps prevent sewer gases from entering fixtures, while air gaps create a physical separation that is crucial for preventing backflow.