Was the area around the hole clear of sand, etc, when you installed the bulkhead? If so, and you have the rubber gasket on the inside of the tank, tighten down the nut some more, but be careful not to over tighten (don't force it). See if that stops the leak. Keep in mind it may take a little while for any water that is there now to dry up, but you should see a stop to drips...
Jack