Well the sediment in the tank turned out to be corrosion

So this weekends job is pretty much going to be sticking my arm down through small holes and wire wheeling by feel!! Joy
On the subject of the forward holding tank I was wondering why hunter did not just glass in a portion of the hull vs the tiny tank that is set in there. Not only would that have increased the holding volume but it would have acted like an emergency crash bulkhead, preventing flooding in case a collision in the bow area caused enough damage to split the fiberglass.