I'm running a single tube for smoke in all my jets and it produces a lot of smoke. I happen to have Jetcat pumps, and a MPI and they all work fine. Other pumps on the market work equally as well. The density of smoke depends on the speed of the pump and speed of the plane. I run my Jet cat pumps on 9.9 V 1,100 ma 123 batteries, and MPI on 6.6V 2,500 ma. You just have to pick a pump speed and match it with your style of flying. Do a little trial and error. I found the Dreamworks tube has a curl on the end and that seems to disparage the fluid more and enhances the smoke trail. I happen to use Robart smoke fluid, but I'm sure other brands also work equally as well.
Bottom line; if you want good smoke your going to go through a lot of fluid.
K.O.