Cool.....so the tube at the end of the gun runs back to a tank with soap? What soap are you using? Have you tried to plug that hose and mix a foaming agent in the chem?
Also....have you found that you use less chem because of less run off? Does the savings of less foam offset the cost of soap?
Just curious...I have always liked the idea of foam on house washes....we use it some when we do roofs...less run off.