A combination of a gal who's an expert at giving killer hand-jobs and a
guy who's so aroused dat he's just about ready to blow when da gal first takes his tautly-engorged
schlong in her hands, and thus she gets him off with just a
single up-down rub.
If a gal has perfect timing with her hand/wrist/arm when performing a 2-stroke engine with a virile dude, it's possible for her to achieve a "synchronized plug-firing" --- i.e., doing the down-stroke on the
boy's cock at the same moment as each throbbing burst of release --- during said balls-draining session. Plus if the
guy's sperm-glands are fully recharged from having waited a sufficient period of time after his last ejaculation, then this "piston-cycle" operation can be performed up to
maybe a dozen times for each successive spurt until the eager
stud finally "runs
dry".