vertical and horizontal tanks
The LPG in your tank is exactly what it says....a liquid. When your valve is opened, some of it can expand, and forms a gas. The gas is lighter than the liquid, hence it rises. Hopefully, the exit to the tank is at the top, so the gas can go out. Vertical tanks and horizontal tanks are each designed to have the gas go out of what should be the highest point. Where you get into trouble is where you tip a vertical tank onto its side, and make it a horizontal tank. In that case, what will come out is not gas, but liquid, which is not what you want! I am not positive of the consequences.....and am not curious! Anyway, where the hose attaches is the top.