Disclaimer: This post was originally posted by Newbie, sgtbob. This was originally posted on December 24, 2011.
I used some old wine corks I had on hand and a piece of wire (light weight shirt hangers), allowed the cork to sit on the bottom of the fill tube in my EB, painted a line at the top of the wire, bored a hole in a cheap plastic cap (any spray paint can top) inserted the wire, filled the EB with water. I am able to see how much water the box needs from the wire protruding from the cap. Not very sophisticated, but it works.
bob