I want to add a hot water recirc line to my trailer

My wife runs the water in the sink until she gets hot water. When dry camping, that wastes a lot of water. I want to run a recirc line by cutting into my hot water line at the farthest point from the hot water heater, put a tee on it and have a switched valved that when turned on, opens and recircs the cold (but warming) water back into the fresh water tank. Does someone make a bulkhead fitting that you can use to insert from the outside and screw it tight from the outside to keep it from leaking? Since you cannot reach into those tanks, there is no way for you to hold a nut tight on the inside. I thought I searched on the net and found one, but I guess I didn't bookmark it. Any ideas?