This may sound silly,. but when I have to take a big crap, when it's coming out, I get the sensation, like euphoria, sometimes. It feels like an anal orgasm!!!
It's not just relief, it's like "Oh GOD!! and I shudder and afterwards, feel relaxed, like I just had a great orgasm. I feel like going to sleep afterwards.
Not always, sometimes it's just a feeling of relief (maybe it's in my mind, because I enjoy taking a crap so much sometimes)
I think a "G-Spot" can be anywhere that gives you an intense feeling of pleasure, more than any other spot. (minus the penis, and clit on a woman)