Why not heat the oil to 150*F, settle for a week holding 100*F, filtering to 5 micornm and draw off the oil from the top, not the bottom of your bulk tank. Oils differ, but my oil held water ... even drawing off 20 gallons in a 275 HHO tank still had some water. Now my oil is fine & once a year I chuck the stuff on the bottom of the tank.
Black crud is algae which grow in diesel or WVO with some water.
Spending more time and $ to remove the water is insurance.
Last spring forgot to purge an old turk style heater in the shop. I knew the oil had some water but in a turk who cares? Well, new 4' fuel line, cleaned the metering valves, pot had 1/2" of tar. This crud was thick, smelly and would not budge with compressed air. 5 minute purge truned into 3 hour !##!#@!$.
Settle, use water additives and biocide.
WVO is not a solvent. Biodiesel is.
If you can't find biocide, call a diesel dealer or marina. This is very common in rich kids boats with crapy dock fuel.
Just be glad you learned now instead of Feb.