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I lifted the front of the boat as high as I could. I took a long piece of stiff plastic tubing and fastened it to a garden hose. I first pushed it through that PVC pipe that drains the tank cavity to the aft storage compartment. I think this will be where most of your problem is. If you get it clean all of that water that is on top of your tank should drain to the box. I also cleaned my utility tunnel the same way because if it is plugged it will overflow into the tank cavity.
Good luck,
Carter