Some glycol-ether aqueous solutions change themselves to be hydrophilic, and then lipophilic according to their concentrations under homogeneous solutions. As the aqueous solutions exhibit phase -transition followed by temperature change, the lipophilic solutions at higher temperature region (e.g. 60 degrees C) enable cleaning of oily dirt adhering to washing materials, and the hydrophilic ones in lower temperature regions (e.g, 40 degrees C) separate the oily dirt dissolved into themselves. A cleaning process is designed, which possesses special features with non-distilled regeneration of dirty cleaning solution and non-waste water, based on the various data that had been obtained for high efficiency and industrial usefulness. Furthermore, a demonstration unit is designed, manufactured and operated for cleaning of various mechanical parts.