I'm not sure about women having orgasms from anal sex alone - I've never heard of it happening.
As for guys though, well yes we can have orgasms from anal sex! But they're different to normal orgasms, from what I gather (I've never actually had one myself either). It's because of stimulation of the prostate. The orgasm is deep inside you, but you cum like crazy apparently.
That's all I know, and it's all based on what i've heard from other people. But, I shall continue trying and will let you know if I ever do have an anal orgasm!
Good luck!
CasperTG

__________________
You know, Blackadder, for me socks are like sex. Tons of it about and I never seem to get any.

My Photos:
https://imgur.com/a/80hiRdm