I could use a little help with my found treasures.I dive freshwater and spend a lot of time looking for (junk) treasures.The problem is that the older stuff has been laying in silty muddy goop. When i get it home the mud looks and acts like cement as in rock hard.How do you get this stuff off.I found a complete dive setup yesterday and just want to make it look good.In case you are wondering the label on the tank is dated 1973.My best find to date.