Your tongue.
I belive a cat is the second cleanest animal,becuse it licks itself every day
no
A pig
Horse
Well, a fly is the 4th most cleanest insect since they are constintly cleaning them selves,believe it or not. A cockoroach is the cleanest ANIMAL/INSECT in the world.
Technically no ones tongues are clean. Not even humans. Living beings whole entire body are filled with all types of germs and bacteria! So that question actually doesnt make sense. Youre welcome! 
Almost every animal has a tongue, And EVERY mammal has a tongue.
No animal truly sweats from its tongue, but some animals do pant to cool themselves in place of sweating. One animal that is known for this is a dog.
Crocodile
Snake.
Crocodiles.