Little prince is on an IV. He has kidney stones. Poor pince. He comes home today. $500 billpor baby. 
And, on diet food after this, because he may be prone to get them. You got him there in time, for cats not being able to pee can be lethally toxic very soon.
Did they operate on him, or have they "just" made sure the stones passed?
I think they said it was a urinary tract infection. His penis was inflamed. Poor little guy. I change his water constantly and yes he is on a diet now. My poor baby.
Stick to the diet food, make sure he doesn't eat anything else, apart from what he catches on life food outside, if he happens to be an outdoor cat.
And be aware, the diet food is very rich, so he doesn't have to eat much of it. If that is a problem for him, you can ask for diet food with more "bulk" in it next time.
Make sure every one makes George keep his diet. Vets are less and less inclined to treat multiple stone infections in cats, because the operating treatment is so hard on cats.
With a diet, things can go really well though. My male cat had the same, a few months after I got him. He's now as fit as a fiddle. Though, he does put himself at risk, snatching food from the neighbours. It is good that winter is coming. Less open doors, time for him to loose weight and stick completely to his diet again.
My vet was less expensive, luckily.
