I should say when I meant the GPs looked good, I figured they would have a whiteish color to them, because of the extra water.
Think your on the right track when it comes to the extra soot on them.
Maybe that "bottom of the barrel" stuff would make good hand washing soap....probably not, being its fuel and all.
Had another thought on your bio diesel stuff, and would be fuel sources.
If you get a chance using a grinding wheel, or a buffing wheel, like a person would use to put a patch on the inside of a tire, get a sample of small flakes of rubber and soak them in some bio diesel.
I know bio diesel really is a good cleaner, so maybe some of the oil that's left in rubber could get pulled out...????
Not that I want anyone to try to burn it yet, but I'm really curious if the bio diesel would do this....
I want to try this one myself but don't have any bio yet, if I do get some bio I'll try this too.
Again nice pics & info.