Today I removed petcock assembly, cleaned filter and mating surfaces, shook/rinsed out the tank over a sink. Blackness. Possibly of satanic origin. ⛽
Then I plugged the hole and poured a mixture of white vinegar + filtered water down the hatch. Shook it up every couple of hours. Drained and rinsed, but I am not convinced. It also left a fine film of rust residue, so I think another vinegar rinse is in orser, this time without water.
Stymied about the RESERVE tank, and how that operates....what is the best angle to tilt to drain it?
I also took some time to work on Ye Olde Dent, which happened several years ago when I whacked the tank in frustration. Ahh...my very-first no-start. #Nostalgia.
Anyway, I popped a large amount of it out. I can live with it for now.