Have a 1988 oceanis 430 which I recently purchased. The previous owner never used the forward water tank, so I partially filled all 3 tanks to insure they functioned ok. The forward tank would not drain to the pump, but the other 2 tanks are fine. As far as I can tell, there are no strainers in the line between the tank and manifold. Is it possible I have an air lock between the tank and manifold and need to prime the line to the manifold? I am not sure whether or not this pump is self priming. Any thoughts? Thanks