I cant see your tank picture, but making a tube is easy. draw a nurbs curve between the two tanks that will serve a a path for your tube, then create a nurbs circle. Select the circle and the curve and go to the Modeling/Surfaces/Extrude options and choose tube, experiement with the profile settings, and read the help. There is a mel script called createTube on highend that will do all this for you, all you need is a curve path to start with...
