I hope Tucker feels better soon!(Black and white cats are tough!)
About getting him to drink more, Phred (Cinder and Smoke) has great advice on it from his own experience with Boots the cat. I think he recently posted in Grasshopper's thread about how to get your cat to drink more with a syringe. Cats like the juice from a can of tuna too, that may help get him to drink too.
Good luck in getting Tucker to feel better soon!