I built my own, at a time when all I could get were cheap bookstore pumps. And minewere every bit as good as the commercial ones. And MUCH cheaper! THey are NOT that hard to build, a decent quality one. DOn't improvise on the tube, go find a plastics supplier and by an acrylic cylinder, glue an acrylic top plate on, drill a hole in the cap of the appropriate size, and epoxy in a brass barbed hose conector. Or, if you want the same quick disconnect connectors as the commercial ones, order some. You can make a flange for the bottom, by using modeling clay, and forming an inverse flange. Stick the dick end of the cylinder into the clay, flush with the flat surface of a table beneath the clay. Mold the shape. Get some casting resin, and cast the flange. GO to an autoparts store and buy a decent quality brass pump with a gauge. VOILA`---a pump package, that you can make in ANY size you want, for about 1/3 the cost of any decent commercial one. If anybody in the US wants sources to go to to places to order the materials, if you can't get them locally private message me and I will be happy to provide you with some links. If you have any reasonable skill with basic tools, you can do it.