Good science has to explain the observed phenomena. I removed better than half a cup of water from a small, vented motorcycle tank that had never contained gasoline or oil, stored indoors, in a desert. Pls explain how it got there.
I did, its called partial vapor pressure equilibrium. What you had is 'old' fuel that became saturated with water, the free water gravimetrically settled and crossed the liquid-liquid phase boundary in the bottom of the tank and started 'pumping'.
Next time close the vent on your tank and see what happens. If you leave fuel in direct contact with atmospheric air it WILL become saturated with water - thats the whole point of my 'discertation'. Again, 'condensation' is the end stage symptom that the fuel HAS become saturated with water.
Either close the vent (on tanks that can withstand the pressures) upon long term non-usage, or 'enjoy' water saturation.