To suck pussy, eat out, lick the cat, eat the beaver. When a man or woman ( i prefer men)burries their face in a woman's hairy or bald pussy and licks her clit with random sucking here and there. A good muff diver knows to focus on the clit and suck and lick it until the woman explodes into a throbbing, wiggling ectsasy. Licking the vaginal opening and sucking on the lips occasionally is a big plus. You can take it a step further and lick the asshole to complete the mission.
One that diver or plunges into the anus (especially a homosexul.) The references is meant to bring forth imagery of a scuba diver in a wet suit diving into the ocean, like a penis plunging into an ocean of ass.
He didn't wear a snorkel but we could all tell that he was an anal diver.
When you are crouched over a toilet (not sitting, standing), and your turd falls about a foot and goes inside the siphon (the hole that shit goes down) without flushing and stays down there without coming back out, without a spash that goes up to your butt hole.