After reading something about a ethanol testing device over on dootalk, I had my local Briggs&Stratton dealer order me a couple. Its a small glass test tube with a screw on cap, about 2oz in size. It has lines and specific measurements on the side. You fill the tube to the water line, then fill the rest of the way to the neck with gasoline. Shake and wait 5 minutes, the separation is clearly visible and the markings on the side of the tube indicate what % of ethanol is in the gas.
Briggs & Stratton part # 795161.
It cost me $7.50 each. (I bought 2)
Here is a link (for reference) I found to a place that sells them. Any Briggs & Stratton dealer can get them for you.