I have a 2002 Fatboy and there is a rubber hose that runs in front of the rear tire. I don't think it is the battery vent. I beleive maybe oil comes out of it?

My question is whats its purpose and what I could I do about keeping the oil film from getting on my bike?

 

Is that a carb model? How big is the hose? It could be the carb drain you referred to.

 

Its a carb model. The rubber hose is maybe 3/8 ID