The function of this hose is to equalize the level of fuel in both tanks. As fuel is drawn from one or both tanks and returned (depending on the engine(s) you have) to one or both tanks, an imbalance might cause your boat to list to the side that has the most fuel.
Did you open the valve slightly (with something under the valve to catch any fuel) to see if anything came out and it is not the valve that is blocked? Did you try the same with the ohter valve? With both valves closed and the hose off both valves, can you blow through the hose? IMO, you should have that hose equalizing system working and it is worth servicing all parts of the system-hoses and valves.