How much fuel is now in your tank? If it's down low enough, you might be able to go under the rig and disconnect the refueling inlet to the tank and place your siphon hose in there. Another approach you could use if you can see a drain plug is to get a hose and barbed fitting that would fit the hole. You should be able to pull the plug, and insert the barbed fitting (temporarily plugged) with the loss of a pint of fuel or less. THen hook up a long drain hose and drop the tank level. After you get the drain plug loose enough to turn by hand, wrap it with a large rag that will keep the fuel from splashing on you. A thumb over the hole and then putting in the barbed fitting can be done the same way. I've replaced an oil pan plug with hot oil in the pan the same way and never got a drop on the ground. Of course the fuel is thinner and will flow easier, but you can do it with absolute minimal spillage.
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