I'm back on the '72 850 restore starting with the electrical and found the fuel gauge low fuel light not working. I had drained the tank a couple weeks earlier of the old fuel that had been in there for probably 20 years. Very stinky. When I removed the sending unit, I found it covered in a black crud, some hard and some soft. Shining a light in the tank, I found it in pretty much the same condition. I would like to clean this tank in place as it looks like I would have to remove the transaxle to remove the tank. Carburetor cleaner seems to dissolve this crud but it would take about $50 worth to get to the level of the crud in the tank. Someone on U-tube suggested toilet bowl cleaner but I'm not so sure of putting a corrosive in there. Does anyone have suggestions for cleaning out the tank in place?