Alligator

A teenage girl's pet baby alligator is flushed down the toilet by her animal-phobic father and it ends up in the city's sewers. Fast forward 12 years, and the alligator survives by feeding on carcasses thrown in the sewer that were used as test subjects for an experimental growth hormone and for anabolic formulas. Because of the effects of the hormones, the alligator has grown massively huge, with a thick skin and an insatiable appetite, and it begins devouring sewer workers that it encounters in the sewer.