I have a small engine shop for the last 17 years in Mississauga, Ontario, Canada.
We have two clear seasons, thus, fuel storage related issues are common.
We consider Stabil a hoax from experience alone.
Theoretically, fuel stabilizers have two alleged functions.
1. These should bind to the highly volatile = explosive components of gasoline and not let those evaporate out of the fuel storage or equipment fuel tank through the gas caps - all of which are designed to be vented. This would enable old gas to start an engine, according to Stabil's claim, for two years, if mixed in the right amount. We have yet to see any two year old gas start an engine. Leave your lawnmower in the sun in the hot humid months, and the engine will not start after seven, even lesser number of days, even if the fuel stabilizer was added right away. Actually, the gas will turn orange with or without the stabilizer.
2. There is the myth of fuel stabilizers preventing the heavy chain hydrocarbons, collectively called varnish, from settling out of gas in long duration storage especially inside carburetors. Absolute nonsense. 95-98% of our work is overhauling/restoring carburetors. This myth is also promoted by many small engine equipment manufacturers. We sincerely believe that every single manufacturer is a crook, including Honda, and they wish that the carburetor gum up as soon as possible, owners break the recoil starters, and burn the electric starters. All these are parts sales. A $2-5 genuine carburetor at the the factory gate sells for at least $100 in Canada. Honda puts stickers on its snow blowers to turn off power switch first, then the fuel cut off valve. Really!
The only solution to prevent carburetor gumming is to install a fuel cut off valve, and turn fuel off after EVERY SINGLE USE. The engine will die in max two minutes. At the end of the season, remove all fuel in gas tank with a siphon (or burn it by running the engine till it dies); crack open drain bolt on the carburetor fuel bowl to drain all gas in carb and fuel line; snug drain bolt; close fuel valve so that any old gas remaining in the tank stays in the tank.
WATER IN FUEL:
We have recovered up to a liter of water from a 5 litre or one US gallon fuel canister. Ethanol is a pure alcohol. It mixes readily with water in air in tank, then this water+ethanol mix interacts with gas, and creates an acidic gel that corrodes carburetor metal. If water is in excess than what the ethanol can absorb, or fuel is ethanol free, the free water will go to the bottom of the tank.
There is a green colored plastic funnel that has a filter in the middle. I tested it. Water does not go past this filter. The method is slow.
Or, once you have removed the water by decanting it, and see no water at the bottom of the tank, shake the tank. If the fuel turns cloudy, water is mixed with gas. No choice but to discard it. Use it, and your engine should suddenly stop again and again.