What works best is a pump-up gargen sprayer with water. Spray on a light coat and let it soak in. It will not "contaminate" the drywall. Remember, you're not hosing it down like you would if it was on fire and you had a fire hose. Water mixed with "Dif" is used all the time to loosen wallpaper applied to drywall with no problems of "contamination". After the water soaks in, 5-10 minutes, use a wide blade scraper and the stuff comes off without much trouble. If the ceiling has been painted the story is a little different. The water doesn't do you much good. You'll have to use the scraper and a little elbow grease.