Bit of a "trade secret" but I use what is in essence a spinning scotchbrite pad and I buff it off - fluffing up the cotton basetape as well. I use the same setup to remove the bulk of glue from rims as well when taking them back to the surface for gluing. I used to also used to do quick swipes on fresh tires to help remove any grease or oil that was on the basetape during handling and shipping if they weren't stored in bags.