When I bought my Bristol it had a 24 gallon fuel tank, full, which had set for at least 4 years. With my trusty little handpump, I pumped the whole damn thing dry, flushed with a couple gallons and pumped dry again, draining as much as possible from the fuel/water separator, but still finding that pumping was necessary. A length of lp gas type copper tubing on the pump makes it a pretty good "wand" for waving around in the tank and getting all the corners. I did get quite a bit of sludge. I simply dumped the diesel into my heating oil tank (in Maine) at home and burned it with no problems. It''s the same fuel, different color. I save the last little bits in the cans, dump it into glass so I can see the water, pour off the fuel and use that for a relatively low volatility paintbrush cleaner. The last gallon or so of crap is effectively waste fuel, which I gave to a friend who had a waste oil burner in his garage. Afterwards, keep an eye on your fuel water separator and a jug nearby to drain a little into every once in awhile to keep the fuel getting to the engine aqua-free. Look for clouds in the separator, schmung in the bottom. It''s pretty obvious. No big pucker.......