PE-- I think you're only partially right about single wash baths because you're not taking into account the relative volumes of emulsion and the wash water. I've purified proteins and other materials using dialysis, and the concentrated side and the dilute side will reach an equilibrium when the concentrations are equal, *but* with a relatively larger volume of wash water--the initial concentration of the solute can easily drop to less than 5% with a single wash after the system reaches equilibrium. Imagine washing 1 ml of emulsion with 1 ml of water vs. washing with 1000 ml of water. If the washing bath is sufficiently large, it performs nearly as well as running water with no solute.