LOL! This is why I have a mare!
Much, much easier to clean!
That said, check out this site. http://www.equisearch.com/advice/how...386/index.html
Many geldings get gunky up in there. It needs to be cleaned out. They can also get what is called a bean in their uretha that needs to be removed. If you don't want to do it a vet will usually do this. Especially if the "guy" is not crazy about being handled there... A vet can give light sedation, then clean. Most geldings love being cleaned, at least once they realize how much nicer it feels afterward!
Stallions also need to be checked. When they um, "service" mares, it gets kind of cleaned, but if they arn't doing that, then they too need cleaning.
My friend has her hubby do the sheath cleaning! LOL! It's done about once a year, usually in the spring along with shots and teeth.