Your ass is not the cleanest of places, but it isn't meant to be. It's the tail end of your body's sewage system. If anal play is something you want to enjoy with your partner, you have to accept that getting dirty is a possibility.
But a little knowledge of how your body works can help you avoid potential embarrassment.
There are different levels of cleanliness to consider based on how seriously you want to play but in addition to cleanliness, it's important to remember your body has it's own bacterial ecosystem that you need to protect.
Getting dirty isn't the only point for consideration. Anal play can also expose you to disease. To avoid illness including sexually transmitted disease, you have to play safe.
The primary function of the anus means that is connected to the digestive tract. Your anal anatomy is a subsection of your body's energy extraction system and it is teeming with bacteria and other microorganisms. These bacteria reside en masse in your colon (a.k.a. lower intestine) and are a huge part of how it works to get your body nutrition.
There are the good bacteria (like what we eat in natural yoghurt) but there are also the bad.
The bad microorganisms include illnesses that result in vomiting and/or diarrhea, such as campylobacter and shigella. It also includes parasitic infections like intestinal worms.
And then there are STIs to worry about. Even analingus (anal oral sex) can expose you to gonorrhea and more.
All of this just from beginner anal play that many people consider normal sexual practice.
Safe Anal Play
The first rule of anal sex safety is that once it touches your asshole: finger; toy; whatever; - it's tainted. From your ass it doesn't go anywhere near your pussy or mouth (or eyes, or nose). I'll repeat that further on because it's an important rule (regardless of what you might have seen in porn) for your health.
Safe Anal Fingering
Fingers are an easy contaminant transfer. Basically, the above rule means don't touch your asshole then use the same fingers on your vagina. This will keep anal bacteria from spreading elsewhere.
You'll also want to protect your ass, so it's a good idea to wash your hands before sex, ensure nails are neatly trimmed, and move slowly and carefully being wary of scratching inside your anus.
Safe Anal Sex
When fucking, it means ATM (ass to mouth) is a circus trick that is best left to actresses paid to endure it. After going in your ass, his cock never goes anywhere else without a thorough cleaning. Or, use a condom for anal and carefully remove it before fellatio. Same goes for your vagina.
Love your vagina. Treat her well. Do not stick anal bacteria in her. She will get pissed off and an enraged, inflamed vagina (from a bacterial or yeast infection) is not fun to live with.
But what about licking ass? Once you start getting into anal play, analingus is a natural progression. After all, if he's licking your pussy, the other hole is a mere tongue's length away.
Safe analingus means some kind of barrier protection. With a little prep, a condom works. Just unroll, cut off the top then insert the scissors in the tube and cut down the length. You will now have a rectangular sheet of latex protection. Or alternatively, a dental dam but really, who has dental dams?
Less safe but common practice among long term, monogamous couples (myself included) is just to wash the anus thoroughly in the shower directly prior to play. This isn't a guarantee, but at least you know you aren't licking up leftovers.
It's a great way to warm up to anal sex (or simply for it's own pleasure), and if you are willing to do in spite of the cleanliness issue I highly recommend it. Lying back with a vibe on your clit and your partners tongue sliding around your asshole is indescribably indulgent.
Is Anal Sex Poopy?
Normally, if you stick your finger up your butt, you would find it empty.
The first inch or so is the anal canal and the tightness you are feeling comes from your anal sphincters. No poop here.
After the anal canal is your rectum which is where you may encounter some fecal matter. But your body doesn't naturally store poop in your rectum. It stays further up in your colon and as soon as it comes down into your rectum, you feel like you need to go!
During normal anal sex your partner's penis is only entering your rectum and so he shouldn't get a shitty dick.
Healthy Poop for Better Anal
Having good sized, regular, well textured bowel movements is a sign of good health and diet. As a side benefit, it also lets you enjoy anal sex more easily.
Getting the right amount of fiber is important in because it helps your feces stay soft and fluffy. Smiley face!!
Soft poop comes out easily and doesn't irritate or scratch your insides. Fiber plays a big part, but is only part of the story. It's also important to go when you need to go.
If you feel the need to poop and just clench until the feeling goes away, that means the poop that had come down into your rectum has gone back up into your colon. The colon keeps doing what it is supposed to do (absorbe moisture from the feces) and eventually what was a perfectly soft, healthy shit has become a hard stool and you may have just given yourself constipation. Not good for your ass!
There are three reasons you might get poop on the dick:
You didn't realize you needed to go.
This can happen but if you know your body and have regular, healthy poop habits it's extremely unlikely... unless;
His cock is really long.
In this case, if he's getting all the way in, he might go past your rectum (where you can feel there's poop there) and into your sigmoid colon (where you can't). However, it's not easy getting deeper than the rectum, can cause pain and or injury and isn't recommended.
Your colon releases poop while you're having anal sex.
In other words, while you've got his cock in you, your body decides it's time to go. But again, this is unlikely.
The reality is, both of you need to accept shitty dick might happen. It most likely won't, but there's a chance.
Anal sex happens in your anal canal and rectum. If there's poop in your rectum, you'll feel like you need to poop. If you don't need to go, you can bet (not with certainty, but with good odds) your anal sex experience will be poop free.
The best timing is a few hours after you have taken a crap. This means you've cleared things out and your body has naturally cleared any remaining scraps away (by pulling them back up into your colon).
Don't let the fear of poop stop you from trying this extremely pleasurable, emotionally intense sexual act with a sexual partner you love. If shitty dick does happen it'll just be a tiny, small smear at first, so if you see it simply stop, clean up and continue with something else. (If you keep going with anal at this point it's only going to get shittier.)
Using an enema prior to anal sex is one way to ensure you don't have to worry about having a shitty anal sex experience.
A small enema of about 1 cups worth of water (200mL or 7 fl. oz.) will rinse out your rectum. A large enema of about 2 quarts or 2 litres will go much deeper and clean out your colon too.
Enemas are considered to be a healthy practice as long as you don't do it too often. Your colon is host to bacteria that we humans need to help us digest food. Using enemas too frequently may upset the balance of all these different types of bacteria, not to mention, irritate your anus.
After taking an enema, you will need to wait some time before having anal sex. First, this is because your anus may be slightly irritated from inserting the enema nozzle. The second reason is that it can take several trips to the bathroom to void all the water. When taking a large enema, the water goes around a couple of corners and may take some time to come out. Give yourself about 3 hours to recover from the enema before trying anal sex.
After using an enema, you can confidently expect to enjoy anal sex without getting poop on his penis. But not only will an enema clean you out for anal sex, it'll also clean away bits of old feces and leave you with a healthier colon, especially when done (not often, but) regularly.
For enjoyable anal sex, and anal sex that is less likely to result in shitty dick, a healthy pooping habit plays a big part. Using an enema can clean you out but it can also be one part of maintaining a healthy colon and having comfortable, regular number twos.
Healthy pooping means going regularly, almost to a schedule. It means poop that is soft and almost fluffy, if you can ever call shit fluffy. It means less uncomfortable gas and farts that aren't super stinky. It also mean you'll have less stomach discomfort related to unhealthy bowel movements.
Getting adequate fiber and just eating healthily all round plays a huge part in healthy poop. As does regular exercise. I'm not saying change your diet just for anal sex, but it does add another point to the huge list of reasons to eat healthy and look after your body.
When all the sweaty fun ends you'll probably still have a bit of lube up your ass. You may also have your partner's cum up there too, if you didn't use a condom. Two choices: push it out or hold it in.
If I have any energy left, I'll walk to the bathroom, sit on the toilet and gently push to force out the lube, maybe some cum, and probably some anal mucus that has been loosened from all the activity.
If I've been fucked to that orgasmic place where consciousness wants to abandon me and my legs aren't able to even consider walking, I just clench up and squeeze the goo up to where I can't really feel it anymore. But I usually prefer to get it out.
But what about his cock? The truth is, most times his cock will come out of your ass clean. By clean I don't mean sanitary or sterile, I just mean with no sign of turd - there will still be ass juice and anal bacteria infested lube all over it, obviously.
The other truth is you have a good chance of eventually experiencing shitty dick. But don't worry, as mentioned it will just be a small bit at first. You get a brown smear of a warning flag. Then all he has to do is get a tissue, wipe it off and it's dealt with. At this point, you should stop the ana. A little bit of poop on his pole is a harbinger of... more. So, back to PV sex. But clean up first!. And get a new condom.