siphon
The fuel tank on my 1984 H34 is well above the level of the main salon sole. I siphoned the fuel through a Westmarine funnel filter into containers, cleaned the tank, and poured the fuel back in through the regular fill port.The siphoning took a while, since I used a small diameter clear hose. This took time, but I felt I had the process under control. And the funnel filter only supported a low flow rate anyway.For cleaning the tank, if you can get the fuel down to a small enough amount, you should be able to wipe the tank bottom with rags, and pick up the gunk with the last of the fuel.