Scrape soap with a knife to make a fine powder then add equal amount of white sugar ...add just enough water to make a gooey paste . Apply to a bandage and place over boil. This will draw the infectious center of the boil and create a "head" in the center of the boil. 

Use a clean sterilized needle to just break the surface of the skin in the center of the boil ( the skin is dead here by the time you can see a core of the boil) Continue to apply poultice once or twice per day . This will draw the core of the boil out .