I can recall this scene that traumatized me when I was around 6 years old. A little boy is awake in the middle of the night, he walks outside by himself for no reason that I can recall. He finds himself behind what I assume is his house and wanders into an opening to a storm sewer or something. In the sewer he finds himself looking at a skinless person or monster. Dripping with slime or blood. I think it was a monster… that was 25 years ago.
Maybe: It (1990) – http://www.imdb.com/title/tt0099864/
Kinda sounds like Return of the Living Dead 2.
http://www.imdb.com/title/tt0095990/?ref_=nv_sr_2