True diarrhea is when the bun produces none of the round, normal poop, just runny poop, often watery and/or with mucus in it. The bunny is very sick and weak and has no appetite. This is rare in adult rabbits, but not very uncommon in very young rabbits. It’s often due to an infestation with parasites called coccidia and needs immediate vet attention, fluid replacement therapy and antibiotics. It can occur in adult rabbits following treatment with certain types of broad spectrum antibiotics that kill off the good gut bacteria and leave the field open to overgrowth of really bad bacteria. It’s a true vet emergency.
Sticky poop is also called intermittent soft cecotropes. The bun has bouts of sticky, stinky poop, sometimes quite a lot of it, but there are also round poops. The bun can need help with cleaning his rear, but doesnt appear sick. The soft poop is stinky because it’s cecal poop, the type of poop the bun is supposed to eat. Persistent sticky poop is as a rule about diet, a too rich diet or a diet with too little fiber in it. Occasional bouts of sticky poop can be due to changes in diet or medicines, esp antibiotics,
Here’s an article about ISC in rabbits:
http://rabbit.org/intermittent-soft-cecotropes-in-rabbits/