I did drain the Kubota RTV's fuel tank. Thought the diesel fuel tank opening was enough to see around in and perhaps get my arm in to feel around. Perhaps when I was 18 that would have worked, but not anymore. Fortunately Evia's arm did fit! Although she claimed she didn't feel anything, her swishing around freed up whatever was blocked... what little fuel that was left in the tank started running out the fuel line. I took the advice of the dealer and used my compressor to blow out the fuel line as well. The diesel itself looked clean. Added a can of SeaFoam just to waste some money, and siphoned the fuel back in. Tada! RTV is working again, at least for now.
One photo of that campfire being made from the previous post: