To break down the word , head refers to getting neck ( having ones genitals sucked). %20bin refers to the amount of nut you have in the "tank". So the term head%20bin simply is defined as , upon getting neck one nuts beforehand ,therefore lasts longer during oral sex.
Nickname given to bales of marijuana thrown overboard or out of airplanes. Origin is reportedly from members of the US Coast Guard in the area of Southern Florida.