I bought my enema bag from Walgreen. Fleet(hope that's the correct spelling) kit, but look for the enema bag that holds about 1 quart of liquid).
I do coffee enemas from time to time and when I liver flush. It's very effective and I prefer it to taking Epsom salt(I have difficulty swallowing the salt because of its taste).
If I were you I would use first only 1-2 tablespoon of coffee in 1 quart water and see how it works and than increase the amount. I personally felt a bit the effect of the caffein, I was more alert for 2-3 hours a bit hyper as if I would have had 2 espressos(that time I made the coffee enema too strong maybe 4-5 tablespoonin 1 quart).
But it's very individual, some people say they caffein didn't effect them the way coffee does when they drink it.
It's a very effective way to clean your bowel.