20-30 PSI is appropriate to carbonate and must remain at this pressure during serving. When you decrease the pressure, the CO2 comes out of solution. Since the pressure is so high, you must have long lengths of beer line to add resistance before reaching the tap. Temperature change from the keg to the tap can also cause a lot of foam. Ensure your tower is insulated and install a fan to force the cold air into it. There are also mixer nozzles that you can install in your OUT tube as shown here at my blog http://swaggerrootbeer.blogspot.com/2010/12/tame-foam.html
You have to wait at least a week for the CO2 to carbonate your brew if your are not going to roll it around on the floor to speed things up which I recommend. I have found that 20 PSI is best for carbonating/serving. Ensure your brew is chilled to serving temp before force carbonating since cooler temp will allow more CO2 absorption.
Swagger Root Beer http://swaggerrootbeer.blogspot.com/