I found this while replacing the belt on my 2001 Sportsman 500HO. I have no idea what it is for. It was not hooked up to anything, just laying on top of the motor. Is it the vent deal for the carb? I see there is a nipple there with nothing on it. The "filter" thing says VAC on it. Here are a few pics of it.

 

Thats a vent line off the carb.....the "filter" is a one way valve to keep water out

 

Yeah it goes on the bottom of the carb on the float bowl.