"I had an anus some time ago... and before you start joking, I'm gay so whatever you say is probably true :D "

Something I don't get is this connection in American Culture between anal sex and gay men. There are far fewer gay men who have anal sex then there are straight men who do just because the are fewer gay men then straight men in general. I suppose the case might be made that proportionally fewer straight men are in the receptive role during anal sex then gay men are but I wouldn't stake my life on that since some ladies like to have their way with dudes and some dudes like it that way. My understanding is that anal sex is engaged in essentially by the same proportion of m/f, m/m, and f/f couples. There are gay men who never have anal sex and straight men and lesbians who could not imagine going without.

I would think the best way to deal with anuses in Poser is with post-work... maybe someone could post a tutorial. The issue would be similar to post-working clothes in that its mainly about showing folds/creases/bulges using highlight and shadow overlays to create the illusion of volume and texture.

As for geometry, it may have been mentioned already but I think it was Casette who said he took a morphing torus and UVmapped it to the figures head or torso to capture texture and used that with post-work blending. I imagine you could add some texture with a displacement map and fade it to the hip with a transmap. A parented prop like this is might actually be easier to pose with then a integral hip.