Hydro dipping?

You don't want the paint to sink when poured in... It has to be thinned or already thin enough that when you pour it in it spreads on the surface of the water creating a thin film. When you dip the part it is only going through this thin film of paint which wraps around the part. This is how you get all the funky swirls and stuff when using multiple colors.

Depend upon what you are going for. Durability or pretty swirl patterns. If you are looking to do the patterned dip I would still prep all your parts with a good rust encapsulator. Otherwise there are much better ways to get a strong coating on your parts than hydro dipping. Chassis Saver, Por-15, Eastwood chassis and even Rustoleums farm implement paint brushed on will be stronger.

I really like getting stuff powder coated. Found that our local drive-line shop would give me a discount if I had the parts prepped and had wire hangers on all of them. So all they had to do was hang up all the parts and coat them when they were doing a big batch. Did the full differential this way. Suppose it only really works for parts that don't have rubber bushings and stuff that can't survive the oven though.

Video of a guy dipping a guitar but will give you a good idea of what's going on:
DIY Swirling a Guitar body with Testors Enamels - AMAZINGLY SIMPLE! - YouTube