The best gas gauge I was able to find was a stick or dowel. Start by making sure your tanks are empty. Then put in one gallon at a time and inserting the stick. When you pull it out after putting in one gallon at a time mark it with a sharpie. Bammm! There you have it, the most acurate gas gauge ever.
On a more serious note DD, my shit don't work that well either. I ran out one time when my gauge said I still had a 1/4 tank. Notice I said "I ran out one time", that shit won't happen twice.