Yeah, one reason I wanted to ask is because I've heard about people spraying it on their joints. But I know that doesn't mean it's okay!! Haha
Water and soap just doesn't work. Because this is a lot of fresh extremely sticky sap. But I might could try dish washing detergent. I know you wouldn't want to use it on a horse too much, but it shouldn't hurt to use a little in the mane. But my horse shampoo has not even touched it.