The "universal solvent" is...
Yep, water. Any other chemicals you put on your hands will enter your tank. Anthony Calfo's talk at MACNA was interesting because he mentioned something specifically that has always been sort of a second-nature, common sense thing for me... If "trace" concentrations of elements down to ppm and even ppb and ppt can effect our aquarium's inhabitants, and we introduce just a tiny speck of perfume or dye or soap, we're contributing to pollution that may even be in excess of 1ppm, depending on the size of the aquarium. So... no chemicals should be used to "clean" your hands prior to placing them in the aquarium. The best solvent to use, IMO, is a good rinsing of tap water, with NO prior "cleaning" (read: contaminating) with ANY soap. If you're doing a water change during this, all the better, what better "cleaner" to dissolve into solution what would otherwise be dissolved into your aquarium, then a bucket of that very water that is going to be discarded anyway? Yep, after a rinse of tap water, why not a rinse of old aquarium water to further dilute any potential contaminants with its more caustic (than tap water) nature?