I remember Mike Phillips once suggested that the best way to get rid of sap on a car is to place a dab of alcohol-based hand sanitizer on it. This enabled the alcohol to dwell on the sap for a longer period of time. So if there is a "clump" of sap in your microfiber or wash mitt, I would try the same thing. The key is to let it dwell for a minute or two before you wash it out.