Fuel vapor canister questions

Taking a few things out of the engine bay to media blast and paint.  One is the fuel vapor canister, just removed most of the 48 years of gunk but two questions.  How does the top separate from the body?  There is a snmall tab you can but out but the top looks like it is snug around the bottom piece and I do not want to prey it or bend any metal.  Also there are 3 openings in the top as seen in the picture.  The largest one goes to the air cleaner of course, the next size down (the one NOT capped) is the line from the gas tank but the smaller port is the one it question.  As you can see on mine it is capped. is this for a vacuum line and if so should it be connected or capped as it is now?  thanks again.

I don't believe  they were intended to  come apart - but having said that, I rebuilt one for my car. I took a small flat screwdriver and slowly and carefully pried up around the bottom of the lip in your first picture.

disassembled, clean and refilled with charcoal pellets from a pet store (bulk fish filter media).afterwards, I used lineman's pliers to bend the lip back down,and then a vise to clamp and  press it tight. I had to work my way around a little at a time, but it didn't take long.

Southern Ohio creative engineering .....