Originally Posted by Barkingdog
Just watch your cat use the litter box and if it has diarrhea you'll be able to tell. The poop will pour out and if you're not finding any stools in the litter that is a very good clue your has diarrhea or is not pooping at all. And poop does smell difference from urine.
How long do you wait for that? xD My cat likes doing his business at night as well! I did find stools. Perhaps fewer than his usual stools though. However, from the fact that he has had some smearing on the box (not very much) and a few drops on the floor, I can only assume he had diarrhea. However, without those obvious symptoms (i.e. I haven't found smears/drops after the first two days), I have been unable to tell if he's passed through the phase or is still having diarrhea. He's also really energetic and is behaving normally, eating etc.
As for the smell, he covers his poop in litter, so its hard to smell it without bringing it close to my nose, which I dont want to do @_@