Hi J.,
My two year old daughter has done this since she's learned how to drink from a cup. I noticed that she does it like an experience type thing. She'll drip it through the sippy part and says "water babies" as watering the plants, than when we learned that she shakes it constantly, its cuz she's not getting enough out that she wants to drink, we also always made her clean up her mess. So we took the tops off the cup and let her drink from the cup then, she drinks about a quarter of it and than dumps it. BOREDOM! Would be the key word. If you just give him maybe a quarter of the drink in his cup without the sippy top, than he'll drink it up or he dumps it and let him know that he's not getting anymore if he keeps dumping the drink out! If that don't change, just let him go with out until he's thirsty. For the clawing, scratching and fit throwing, maybe there's ways his mom deals with things at home. Ask her what she does when he scratches or hits or claws people and throws his fits. If she doesn't have any clue and she doesn't give you ways to deal with it, than I'd let her know that you can not watch him anymore until she cuts his nails, teaches him its not nice and he can't always have his way, but that's typical for any 2year old. My daughter pulls her sisters and dads hair when they don't pay any attention to her. Or she screams or shuts the tv or computer off on all of us. So what I do is ask her what is it that she wants? First off, than if she scratches, hits or pulls hair than I tell her that it hurts us when she does it, she tells us that she is sorry and she'll tell us that she wants to play or she wants to eat or drink something! But when she realizes that she did do wrong, she does kiss the spot where she hurt someone and appologizes. I have only set her in time out one time, due to the fact that she made my 10year old bleed, and cry. I told her that she is in time out for 2 minutes because she has hit her sister and made her bleed, that its not nice to be mean to people especially when she wants to play with them. I left her on my bed for 2 minutes, she came out to me and said she was sorry. And she was in a better mood after that. I told her I wasn't mad at her, that I was just sad because she hurt her sister. Ever since than, things have been different. She hasn't been spilling things since we don't use the sippy part of the cup!I do agree with some of the women, Praise him and show him love and let him feel like he's at home. If that's too much for you, than maybe its time for his mom to find someone else. Good Luck!!