That's exactly how I cleaned the fuel tank out on my old chain saw the other day! I had left it out and it got water in the gas tank. dumped out the fuel, washed out with fresh fuel and then poured in some rubbing alcohol. swished that around and dumped. made the tank perfectly clean where before the water that had gotten in there had turned all the 2 cycle oil to milk curds.
you'd be surprised how much water a small amount of alcohol will hold!
To be scientifically accurate: you have to know the type of alcohol, the hydrocsrbon average weight of the specific fuel at the moment and the specific gravity of the bio stock.
But the generic measurement is: it’s own weight by volume & the reciprocal of the bio masses weight.
So basically the same amount of alcohol there is.
Imagine the manufacturer makes 1 gallon of fuel containing 25% alcohol.
It can suspend 1 quart of water.
So if the fuel station has leaky lids, and it’s a rainy day, you buy 25 gallons of “fuel”.
You actually get 20 gallons of fuel and 5 gallons of water.
Sounds insane right? But, ya know, physics and all.
Ask me again why I hate corn fuel.
Because 100% pure ethanol is now considered BIO fuel.
Why? Because the corn was a plant (live plant or animal = bio)
So our friend in Illinois can be getting 80% fuel & 20% ethanol delivered to the gas station, then that 20% absorbs 20% water. Poof! Do the math. He now gets 60% fuel, 20% alcohol & 20% water.
Science is fun!