Olive Jar Test for Alcohol
By: Ed Burkhead
You can pre-test for alcohol at the gas station. Here's a review of the olive jar test for alcohol.
Empty and clean a long, thin olive jar and keep the lid. (Actually, any tall, skinny container will work as long as you can see through it.)
Watch out for pumps that share a single hose for all their fuels. If some of those fuels have alcohol, you will get some contamination even in their no-alcohol fuels.
If they have separate hoses, you can make the test before you fill your fuel cans.