I remember an interview Belladonna did a while back. She mentioned that she wouldn't eat the evening prior to a shoot and the following morning give herself a couple of enema's (3 if I'm not mistaken), and after the shoot she'd gorge herself crazy with food. When you think about it, the Pro's just consider it "a part of the job" and not some extra special activity they are doing for the benefit of the other performer(s). Makeup, shaved/trimmed pubes, and no poo in the backdoor (if it calls for a scene).
From my experiance, I've suggested "butt love" (sounds more cuddly and silly than does ANAL SEX) to a couple of partners and not had a problem. I suppose I had been lucky since one did not have a problem with it, and the other had a slight reservation, but since she knew I was into it (pardon the pun) she agreed. That one came with a Quid Pro Quo clause, for which I didn't have a problem fulfilling. I must agree with the previous posts, communication is the key. You gotta tell her that first and formost you would never do anything to hurt her physically or embarrass her, and that if the mere discussion of the topic gives her the willies that you'll drop it. If she gets that "oh brother, here we go again" look on her face, drop it and don't mention it again. but if she gives you 3 minutes to speak your mind, tell her that how much you'd like to "experiment with something different in bed" and that you feel "so comfortable with her, that you can ask her this without feeling like a fool". I wouldn't talk about backdoor bumping while in the good company of others or while standing in line at Burger King. She'll automatically go into defense mode. Rather, while you guys are kissing and fooling around just mention it, but do it gradually. If you just come out and say "I wanna do you in the butt", she may give a knee jerk response and say "like hell...".
I do suggest you do your homework and research the topic on the inter-web. She may have questions such as "will I be too stretched out and not able to hold my poo" or "is there any perminant damage". Both questions I have been asked, and it's good to come knowledgable to the table and know what you are talking about, than to just Forrest Gump your way into it. Just remember, the first time you do it, do it Slloooooowwww and Easssssyyyy. Don't try to tickle her spinal cord with your schlong or try to reinact a brutal Taylor Rain scene, becuase it only takes 1 bad experiance to turn her off forever. Infact, at the first moment you see she's experiancing discomfort, ether go slower, or stop for the evening and try something else. The main thing is that you don't want her to feel like you are using her "only to get yours". Your chances are better if she knows you are patient, concerned with her comfort, and that above all she has the ability so say no anytime without you going into a whining tirade.
Good luck
ps, don't forget the lube! use LOTS of it. The rectum wasn't designed for sexual activity and does not lubricate itself. The inner walls are very tender and tearing is possible if done incorrectly.