OK, so I now have a few tanks. HOWEVER, I have decided that there are advantages and disadvantages to what I have. I have a tank that has plastic top and bottom, but the bottom has a correctly shaped fitting for a carto that is flanged at the bottom. In other words, it has two straight sides and two rounded sides so that the carto "locks" into the bottom, which makes tightening the carto onto the PV easier. I also have tanks that have a metal top and bottom stopper, but the inset on the bottom is completely round, which makes tightening the carto more of a challenge. I'd like to find a tank that has the metal top and bottom, with the correctly shaped bottom stopper for the flanged cartos. In addition, I'd like the metal to be BLACK, and the tank to be dark. Suggestions?