a liquid - dispensing nozzle has a system for blowing air for a period of time through the nozzle &# 39 ; s spout after the liquid valve closes . the flow of air purges and expels most of the liquid adhering to the interior surface of the spout , preventing this residual liquid from contaminating either the ground on which it may fall when the spout is withdrawn from a filler pipe or the air through evaporation . the invention applies particularly well to dispensing of liquid fuels such as gasoline .