I agree. Don't use it to solve the problem. What about using it to test for the problem? It won't catch all situations but it is probably safer than using a multimeter.

NO

A ground probe only creates a path for current your not measuring anything. Multimeters are built to safely measure voltage (within the rated capacity of course). Now to measure current that's a different story, but to check for stray voltage you will still want to use a meter.

Red lead and black lead off the meter, doesn't matter which you want to use for what, one goes into the tank water the other into the ground of the electrical plug. (the ground is the half circle in the middle in case anyone doesn't know)

Just check the voltage rating of the meter before you go to use it, make sure it can handle more than what you are testing for. My personal Meter for the job is rated at:
CAT III - 1000V rating
AC Current - 660A
DC Current - 660A

Similar to this one
http://www.homedepot.ca/product/clam...cat-iii/930198

doesn't need to be an expensive one but needs to be able to handle more than you want to test for.