The dirtiest and filthiest place on earth has got to be Pakistan since it's the most polluted place in the world.
Also parts of India have some pretty filthy streets and places so that would be the second filthiest place on earth.
Parts of Baku, Azerbaijan are pretty filthy and have A Health and Sanitation Index Score of 27.6.
Besides Pakistan I would say that India is the second on the list for being a pretty filthy place as you can see by photos of typing in Google Image search of India Dirty Streets.
Here's a photo of some parts of India and there streets.