blue, there is a fill on the port side at the rear of the tube. I was going to put a fill pipe on the gunnell rail, bur decided to just put a pvc cap on a stand pipe. to access I just lift the transom hatch and fill. it flows to both sides equally. on the cap toward the bow end of the tube i put a vent hose. it works great, both sides draw down equally so balance is not a problem
this is the fill
the 3" pvc fits snug between the liner and outer hull on the deck supports. I did take some plumbers strapping(thin metal straps with holes) and tied it to the liner inside the rod boxes. I also put a piece of carpet where the tube touches the outer hull to keep it from rubbing. hard to explain, next time the rod boxes are out i'll take a pic.