In his first ever “talkie” tutorial, (finally) normal voiced Dave Girard shows a method for creating a hollow object filled with liquid in Maya, demonstrating a simple way to have the refractions appear to render correctly by making some simple tweaks while modeling the objects and in this tutorial Dave shows his workflow for modeling those simple tweaks.
If you’re rendering a liquid inside of a transparent object, there’s no easy way to fake the thin wall and liquid – they have to be modelled so that they render correctly
When rendering lets say a glass that has liquid inside of it, a problem arrises with the two surfaces that will have two different refractive values that essentially share the same space. For example, the wall of the liquid object will sit directly against and share the same space as the wall to the inside of the glass.
Dave makes note to another tutorial from Spot3D that deals exactly with this problem more in depth when rendering with V-Ray, Rendering Surface Interfaces.