Denatured alcohol isn´t usually a good choice, because it´s usually like 60% or whatever alcohol, the other 40% is water. 98% methonal works well, you can usually get some at the pharmacia, it´s usually cheaper if you bring your own container. 400-500 mililiters or a pint is the usualy dosage (for a fulll tank of gas). Not a good idea, to use the methanol any more than you have too, it will eat up some types of rubber/plastic (over the years).
A little water doesn´t really hurt much, it´s when it collects in the bottom of the gas tank, that it causes real problems.
A good solution, I´ve tried on my YJ, is to install a really large diesel fuel filter (like a quart and a half), most of the moisture (water) that falls out of solution, will collect in the bottom of the filter. The diesel fuel filters, usually come with a valve in the bottom, to bleed off the excess water/moisture, without having to open the filter. I use a mil. spec. filter and element, specifies either mo gas (gasoline) or diesel. Doubt a regular diesel filter would cause any problems with gas, but may be a bit coarse to filter much out of gasoline, but will still work, to help seperate the water out.
Haven´t seen one in years, but a transparent fuel filter will let you see whats in the bottom of the filter. A filter to seperate water has to be fairly large, like a guart/liter in capacity to work well.
