Are you sure the fill line didn't crack? This would allow water to spill out as you were sloshing around down the road.
Isn't the tank under the step to the overhead? If so, just remove the step and than the panel in front should be removed with a couple of screws and a long bit.
To remove the tank, there is an access panel on the bottom which will allow you to disconnect the drain line on the passenger side of the tank. Fill and water line are accessible from the kitchen cabinet on the drivers side or after you pull the converter out.
Above based on the 815 which is the more modern version of the 3000.