When assembling a tank try soldering on the Dubro barbs, they come in several sizes and are cheap, they will keep your lines from falling off. Try using fuel line over fuel line to attach your lines to a tank. This doesn't work usually for any lines that need to be removed to fill or empty a tank, it really makes a nice tight fit. After you assemble a tank check it buy pressuer testing under water. A hole in the lines either inside the tank or outside the tank will cause bubbles. A pressure line inside the tank that is upside down will cause you to not get a full tank of fuel.