Mechanical blocking plugs with a bypass provide a seal inside or at the end of a pipe to block flow and allow for pressure testing, maintenance, or to prevent unwanted material from entering the pipeline. The bypass is a removable cap that allows flow around the plug and helps release and clean out material that may have accumulated inside the pipe. These blocking plugs have a manual closure mechanism that squeezes two plates together to compress and expand a seal that presses against the internal walls of the pipe. They are primarily used in drain, waste, and vent (DWV) systems.