HEET:
• The #1 brand for fast cold weather starts, and year-round water removal.• Safe for use in all 4-cycle engines, including fuel injected engines.• DO NOT use in 2-cycle (gas and oil mixture) engines, or in diesel engines: use Iso-HEET instead.• Prevents gas-line freeze-up. Removes water from fuel system.• Prevents rust and corrosion.______________________________________________________________ISO HEET
• Absorbs 5 times more water than regular gas-line antifreeze.• The #1 brand for fast year-round starts.• Safe for use in ALL 4-cycle and 2-cycle gasoline engines, and in diesel engines.• Use year-round to remove water from fuel system.• Prevents fuel-line freeze-up.• Prevents rust and corrosion.
Source:
http://www.goldeagle.com/heet/products.htm
But you should use ISO HEET every fill up as a NICO guideline.
Best way to remove crap form the bottom of the tank, is to remove the tank from the vehicle and thoroughly clean it.