1970 Chevelle 396

Thank you guys! I’ll post better pics when I see the car again in a couple hours. Sorry for the bad first couple of pictures but I figured I’d still post it in case someone was able to recognize it. Max, that would make a lot of sense as I believe there is only one nipple on the entire jug and that is why it confused me as being an evap can.
Well, if that's the case I wouldn't hook that to vacuum.