OK, the tank is NOT coming out. After an hour with a sawzall, a jig saw and an angle grinder, jammed in a 20 inch high space I had removed the top of the tank. The rest would have taken two years, 4 fingers, possibly an eye and part of an ear. An the saying goes; "He who fights and runs away will live to run away another day". I am now the proud owner of an aluminum lined, bilge, rum storage cellar.