How to partially fill a box or container

Question

I'm trying to make a graphic using Windows Forms in C# to show contents of a flask incrementally decreasing.

I tried using a completely filled panel or a rectangle and just making it shorter.  Unfortunately, location is referenced to upper left corner of Form1, so it shrinks up instead of down when I re-size the object.

 A progress bar came to mind, but can I increment negatively to make the bar shorter?

Perhaps a single bar, bar chart.

Anyone have a straight forward solution?