If it is a cleanse, it is useless to treat pouchitis. The only valid reason to do an enema, other than taking therapeutic enemas such as Cortenemas or Sulfasalazine enemas, is to flush the pouch in anticipation of a pouchoscopy or other exam. Cleanses are not valid treatment of IBD.
For flushing purposes Fleet enemas, although they can mildly irritate the pouch, contain a saline solution that draws water into the Pouch. As such the flushing mechanism may be better using the Fleet saline solution than tap water, although tap water will give you a flush out. The Fleet enema is intended to be held for 5 minutes (and I can usually do that easily), and during that time water is drawn into the bowels which provide additional flushing action.