For those of you who are within relatively convenient driving distance to a NON-ETHANOL gas station, do yourself a favor and ONLY use NON-ETHANOL fuel, including in your cars and trucks. For those of you not, sucks to be you, sorry.
Sea Foam is the most effective additive I've seen operate, as a mechanic, I've used many different products, Sea Foam is the only additive that I've used that you can actually see emulsify the water in fuel (clear fuel filter) and make it usable through a carburetor.
For those of you who are using NON-ETHANOL fuel AND use any given product (Sea Foam, STA BIL, etc.) every time you fill your tank, you're getting suckered.
If at the end of the season you filled your tank, added Sea Foam, ran the motor long enough to make sure it ran through all the fuel system, then sealed everything up and parked it, you should have little to no trouble starting it the next opening season.
Opening season comes around, you take it out the first time, assuming it starts and runs fine, you should run your tank to as low as possible (better yet, suck it dry), fill it back up with NON-ETHANOL fuel, add the appropriate amount of Sea Foam for that tankful and not ever have to add anything else until the end of the season again.
Why?! Because you're using a fuel that DOES NOT attract water, and just because the boat is ON the water, it doesn't substantially attract any more water than your car or truck.
I will fill my fuel tank many times this season, but not add any more Sea Foam, because my fuel tank will not have a long enough duration to attract any substantial water.
STOP WASTING YOUR MONEY ON ADDITIVES EVERY TIME YOU FILL UP.
IF, I said IF, I had to use ETHANOL fuel I would add the correct amount of Sea Foam every other fill up and definitely at the end of the season, but not every time.