Wash them, outside and away from any fire, in gasoline. It cuts the fat quickly. You could use any solvent from kerosine on up but gas worked for me for the 2 years that I messed with wvo. Once the bags feel clean, no slippery fat feeling, wash them in hot soapy water. There are a number of industrial soaps or just use large quanties of cheap laundry detergent. Actually you don't have to wash them in water since the gas will disolve the fat.