I have been interested in buying a kong for Jasper, and until a couple days ago, I had NO idea that you put stuff in them lol but now that I know, it seems alot more interesting, and Jasper would do ANYTHING for treats or peanut butter

BUT I would like some more information on them, like what size kong is good, AND exactly whats best to put in them, because with me, I would end up buying one, bringing it home and then not having a clue what to do with it And with things like peanut butter in them, are these hard to clean?

Thanks