tips for anal: use the bathroom well ahead of time, and don't eat anything beforehand. Using an anal douche will make using the bathroom easier, you'll flush out your system more thoroughly, and in general just make things cleaner.
Douches are not highly advised for anal prep, cos it can dry out your anal cavity and can causes infections.
Many people try to make an end-run around the mess by having the woman douche before having anal sex. While douching will clean out the anal cavity and may even feel good to some people, excessive douching can dry out the anal canal and cause micro-abrasions that make passing sexually transmitted infections (STIs) more likely. If she goes number two before you get started, the mess should be minimal. (Source: http://www.askmen.com/dating/love_tip_500/548_anal-sex-prep-guide.html)
Though this only refers to douching too much, I still personally wouldn’t use a douche to flush out the system. I do agree with using the bathroom ahead of time and not eating anything beforehand.