Consumer Product Goods Product Design

I'm inventing the Palaki. The Palaki is a girls best friend. It's a consumer product goods beauty item that is a hand-held hair brush with a liquid compartment that stores your favorite leave-in conditioner or liquid. Right now I've hacked together a couple mock-ups that represent the looks and functionality of the product and the next step would be for me to create a real 3D model of my product so I can 3D print a few models and see what mod's need to be done before developing a working prototype. I'm also looking for additional design guidance. I'm looking for design idea's on the liquid compartment and how to refill it. This compartment is located on the backside of the brush. A spray button to disburse the liquid will be integrated into the top with a spray nozzel fit in as part of the design. I've pulled together a set of images of the prototype I have so far. As an end result I'd like a 3D image that's to scale and accurately shows the functionality of the product.