Well, the only "plug" on the bottom of the Onan carburetor is the fuel-shutoff solenoid (anti-backfire solenoid) which fastens the carb bowl to the carb body. There is no separate "drain plug" as such. The solenoid screws directly up through the center of the bowl to clamp it to the body and it is this item that you unscrew to remove the bowl. You can certainly unscrew the solenoid and it will drain the carburetor bowl. You will see two wires (one red, one black) going to the solenoid that you must unfasten before unscrewing the solenoid--they are the 12-volt hot and ground that activates/deactivates the solenoid when starting or stopping the genny. The red connects through a spade terminal, the black has a ring terminal that screws to ground. Unhook those two, and you can unscrew the solenoid to drain the fuel.
Mike
