I have a toilet mesh here. I'm trying to find a way to fill up my toilet bowl with water. Any suggestions? I'll give two pictures of the mesh.
In Edit Mode select an Edge Loop at a location where you want the top of the water to be.
Duplicate it SHFT+D Then separate it by pressing P > Selection.
TAB into Object Mode and select the object you just created (I hid the other objects).
TAB into Edit Mode and Extrude these vertices inward as in the imageE SSHFTZ
Select all of the vertices except the outer edge and move them down a bit G Z This creates the "meniscus".
You will want a Subsurf Modifier and Smooth Shading.
Here is my Node Setup for the material.