The Reverse Fountain is
essentially just the regular Fountain pattern with reverse Two-in-one
throws, such that the balls travel from the outside of your body to the
center. Since balls from each side are thrown toward each other in this
pattern, it is slightly more difficult to learn than the standard Fountain.
Before trying the Reverse Fountain, it is important that you are able to do a reverse Two-in-one with each hand.
To begin practicing the full pattern, start with two balls in each hand. Throw one ball from your dominant hand as if in a reverse Two-in-one, and then throw a ball from your non-dominant hand in the same fashion. As the first ball reaches its peak, throw another ball from your dominant hand, and then do the same for your non-dominant hand. Then catch the balls.
Practice this until you can make all four throws accurately. Then it's just a matter of adding in throws and soon you will be juggling the Reverse Fountain.