I seem to be well versed in this one right now. I'm going through the same thing with Pouncer. Can you roll him onto his back and then press gently on his whole belly, increasing pressure all around? If he screams in pain, you know he's blocked and full. MY vet assured me that you'd KNOW if you felt a full bladder. I kept feeling like a complete failure because I could never tell, but it turns out Pouncer was passing little itty bitty dribbles of pee all day long.

Is he in an out of the litter box all day long? If he is in the box, is he there for a long while? Is he obsessively licking his "privates"?

All those symptoms are sure fire clues that he's got crystals and/or he's blocked.

Pouncer and I send lots of good wishes to Max.