Regarding gunk in the fuel tank, I have these experiences.

[Sapientoni]

My Mustang 1700 was about 15 years old when I bought it. I could run it for about 30 minutes and it would begin acting like it was running out of fuel. Pulling the choke out would give me another 2-3 minutes before it conked out. There was adequate fuel in the tank. I would add more fuel and in the 10-15 minutes that took, it would usually start and run again. I began cleaning the fuel system, added a sediment bowl in the fuel lines, put a new inline gas filter. No difference. I noticed while trying to "clean" by scraping the tanks there seemed to be a tar like substance in the bottom. At first I thought, this must be a factory sealer, so I didn't bother with it. Then one day I added fuel from the lawn mower can trying to not run out of fuel. Within a minute the machine began running like crap. I thought this must be related to the fuel I just added. I got 5 gallons of premium fuel and added that to the tank. In minutes the 1700 was running great! Nothing but premium after that for the Mustang. Years later I'm working on a car that had a plastic tank and fuel issues. It had sat for some time and I found a 10 mm return line from the fuel injection had developed a "plug" about 1/2 way from the bottom of the pipe. There was also a tar like residue in this plastic tank. Acetone would not dissolve it. I had the tank out of the car and when acetone wouldn't dissolve it, I tried "Krud buster" from Tractor Supply. That and hot water dissolved the tar and cleaned the tank. Maybe any detergent would work with hot water. Apparently the tar is something that settles out of gasoline and creates a solvent resistant sludge in the bottom of the tanks.

Just a FYI in case you are doing fuel system explorations.