I am getting ready to put a '77 Alfetta back on the road after 12 years of storage. So, I want to drain the fuel tank. I took out what I assume is the drain plug on the bottom of the tank where the line comes out and goes to the filter, but only got a couple of dribbles of gas. The tank is nearly full, and fuel spills out of it if I try to take off the filler pipe. What am I doing wrong? I have a full set of factory manuals but can't find them and I'm completely perplexed!