If you love sliding your dick in and out someone's ass, be cool about the fact that it may on occasion trigger something.
The whole enema thing is an urban myth anyway...
emptyclosets.com/home/pages/resources/health/getting-clean-for-anal-sex.php
Enemas were created as a temporary solution to the medical problem of constipation.
Unfortunately in the early 1900s two fashionable ideas saw their use spread to the general population. Firstly, the idea that regulating your child bowels through the use of regular enemas would reduce masturbation (myth). Second, that regulating your own bowels through the use of enemas would avoid the need to go during socially inconvenient times (terribly important when you want to impress the well to do!).
This second idea revealed the downsides of interfering in your normal bowel function. Overuse of enemas results in the bowel failing to function normally and you become dependant on them.
For gay men, the belief in enemas and douching stems from the urban myth that the rectum is constantly full of faeces and that anal sex = poo pushing. Poor diets and poor bowel habits only reinforced this fallacious need.
During insertion of a douche or enema trauma to the rectal tissues can occur resulting in pain during anal intercourse. Additionally the chemicals of a douche can cause a low-grade irritation that only becomes obvious during anal intercourse. It may be that you don’t enjoy anal sex because you’ve douched!
"But I only use water"
Using water only still removes the mucus lining of the rectum that may have a protective function. A number of commonly available sexual lubricants have been shown to cause irritation of the rectal tissues and an intact mucus layer reduces this.
There are a limited number of studies that show an increased risk of STI transmission following douching (mainly HIV & hepatitis studies). There are a larger number of studies that show microscopic damage to the rectal mucosa following douching and from this there is biological plausibility for the concern about probable increased risk of STI transmission.
The recent abandonment of a microbiocide study (for vaginal intercourse) due to increased transmission of HIV from microscopic changes induced by a chemical that seemed quite safe reinforces the concern and biological plausibility that douching could lead to an increased risk of STI transmission.