Sending unit has weird vent thing

Mopar never made a two nipple sender. These are aftermarket. If you have a later model (some 70, some 71, and all after) that has evap emissions controls, these cars vary. But all end up with a line from the tank vent system coming into the engine bay and connects to the "carbon can" evap system

You can just plug the sender fitting. If you ever build an anti-vapor lock system (they work!!!) you can use that fitting for a return.