Illustration Courtesy of Jack Morin Because of a sphincter and a sharp curve between your rectum and your colon, it would be very difficult -- if not impossible -- for a penis to penetrate the colon. Therefore it's unlikely that your partner is actually ejaculating in your colon. He is most likely ejaculating deep in your rectum. You asked about non-STD risks, but I must point out that the risk of becoming infected with HIV and other STDs through unprotected anal intercourse with an infected partner is high. Your risk is increased by the fact that your partner always ejaculates inside you. Withdrawing before ejaculation might lessen somewhat your chances of becoming infected. Your non-STD-related risks are minimal and can easily be further decreased. To prevent other infections, avoid any oral or vaginal (if applicable) penetration involving your partner's penis after he has penetrated you anally -- unless he puts on a new condom or cleans his penis carefully in between. There are germs that are harmless in an anus but very dangerous in a mouth or vagina. Anal sex can involve friction leading to abrasions within the anal cavity where the membranes are quite delicate. Using plenty of lubrication such as Probe, Wet, or ID will help you avoid this -- as will a slow, careful entry into the anus. Remember, never use an oil-based lubrication such as lotion, baby oil or Crisco with latex condoms. If his entry or thrusting into your anus causes you severe pain, this is a sign that injury is being done and you should consider slowing down, using more lube or trying some other activity. This is one reason why using drugs that decrease your awareness of pain during anal sex is a bad idea. It's also a reason why good verbal communication with your partner decreases risk of injury during any sexual activity. In addition, keep in mind that sexual arousal will make it easier for you to relax your sphincter muscles for comfortable entry. Stories of people permanently damaging or weakening their anal sphincters through frequent anal sex are myths. Anal sex does not lead to an inability to control bowel movements. | 
