I enjoy anal sex immensely... First off be safe. Second use lube. Lots of it! I would recommend your girlfriend wash and be sure she is 'vacant' back there. You can use a lubed finger to gently investigate her backdoor. I like to give rim jobs and have yet to have a 'foul' experience. Timing and communication are the key ingredients there. Take cues from her on what she likes most... rimming the edge or forcing your tongue in deep. Play with her pussy and clit while you rim her ass. After a bit of tongue work, bring a finger into play, maybe two if she can take it. Keep her clit stimulated, but watch her for signs of over stimulation. Keeping her pussy happy when you first insert your cock in her ass will help keep her relaxed while it slides in. If she says stop, do so immediately and ask if she wants you to withdraw. You may want her to sit on top so she can control how fast it slides in. Experiment and find out what works best for the two of you, but put her comfort first and you'll find that you'll be pleasured as well. Good luck!!

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Clever? Nah, I ran out of that years ago. But if you find this, let me know, k?
"The road goes ever on..." ~ Tolkien

In memory of my friend skip...
Go then, there are other worlds than these