Hello Joe, Typically when you have a whirlpool type tub, there is either a built-in air switch on the tub that will turn the tub motor, on and off, or the tub needs to have a wall switch to turn it on and off.
The switch has to be located so it is at least a minimum distance of 3-4 feet from the edge of either a tub or shower stall, and it must be connected to a GFCI protected circuit. Normally any whirlpool tub requires a separate dedicated 20 Amp 120 Volt AC circuit for proper operation and to meet code.
I believe that the female plug is for an optional, in-line heater that can be installed into the tub unit. You should be able to check the installation manual that came with the tub to verify the proper wiring required for your specific unit and model.
I would contact the manufacturer to get a copy of the installation guide and instructions for your model, so you are certain that it is properly installed and the wiring you are using meet the NEC (National Electric Code).
Here is a link to the Mansfield web site with some FAQ's and their phone contact information.
I hope you find this Very Helpful and best regards!