I once read an article in Blues Revue(I think) which spoke on this exact subject. I can't remember much, but here is what I know. To get the "caked on slime" off the harp, use a toothpick, toothbruch or any other such samll utensil and do as best as you can. Don't soak the harp in anything because soaking the reeds may cause them to warp. However, your saliva moistens the reeds anyway so I'm not really sure on that tip. However, harps are relatively cheep. If you mess one up trying to clean it, it is not that big of a deal. Also, if you can help it, bruch your teeth before you play. It may become anying to do every time you play a riff but it will certainly help. Something to keep in mind is that a lot of professional musicians are quick to throw away a harp when its goes out of tune. We amateurs keep the same harp for a lot longer.

Andrew