Both my girls LOVE having their teats rubbed. So every time I groom them, I rub the gunk out. No water or soap or anything. They think they've died and gone to heaven. =]
Gracie didn't care for it much at first. She didn't like her belly touched at all. So after she was thoroughly worn out from the cross-tie battle, I rubbed her belly until she quit making an ugly face, then her belly button, then around her teats. Then I started picking out the nastiness, she decided she REALLY liked it, so now when I rub her belly button, she's already got her lip going, lol.