I'm not the receiver of anal sex, really, but a finger or something else in the anus is a powerful way to convince me to cum sooner. I also enjoy the sheer feeling of clenliness of a good enima from time to time.
I use an ear syringe (like this -->
http://www.drugstore.com/products/pr...UY-PLST-0-SRCH) because its a soft rubber rather than the hard end of a water bottle. Since its a 'medical device' and made from that special rubber it seems to make sense to be able to clean it rather than a water bottle too, but you can't really see inside it either. Oh well...your milage may vary, but that's my preference...