"I need a VERY simple explanation of how to check the possible current through the tank stuff you suggested."
Set the meter to volts dc. Check a couple of known things as a test and practice. For instance, put the red lead on the batt pos and the black lead on the batt neg to get battery voltage. You should see 12v + or - about 1.5. Switch the leads and you should see the same voltage with a (-) . With the red lead on the pos terminal of the battery, put the black lead to various metal surfaces on the bike. This will show you what is a good ground. You should see very close to battery voltage with a good ground. This is because the battery negative terminal is grounded to the frame.
Then, put one lead on the tank where it was touching the line, and the other end to ground as just determined. (The neg post of the batt, or any bare metal part on the frame, engine, etc.) The lead on the tank needs to touch bare metal as was present when you found the problem. Do this first with the key off. You should see no voltage. Next test the same with the key on and run switch to "run". Finally, test with the bike running. You should not see voltage during any of these tests, although I suspect you may after hearing your problem description. If you see a reading it means there is a short in/at the tank. This means that a power source (to the fuel pump, sensor, etc.) is getting from the wire or the component to the tank itself. That electricity will seek the path of least resistance, which apparently it found to your oil line (or whatever line was rubbed through.) I would do these checks before you add the new grounds, if you haven't already done them.
So, what do you do if there is voltage through the tank? Unplug the connections to the tank one at a time until voltage goes away to find the source.
Good luck; post again if you run into questions.
MQ