Vapor/Charcoal Cannister

Thanks everyone for the replies. I agree it hasn't been addressed. I searched like crazy and couldn't find anything.

Here's my sweet piece of 70's engineering. How doe the bottom piece come off? Screw? Pop? I've seen those little filters for sale on eBay.

I've also read that some people put a filter inline on the vacuum...so as the charcoal breaks down it doesn't get sucked up the line. I want to keep mine as I think it serves a purpose and costs zero performance. Besides it's the least I can do for the environment since I'm dropping a 440 into my enviro-machine. LOL