Abstract: A tank [A] has a fluid inlet, a fluid outlet, and a closure [B] wherein the tank may be positioned in line as a pressure vessel. A magnetic core assembly includes elongated permanent magnets [C] and magnet covers or tubes [D] constructed of non-magnetic material for collecting magnetic particles from a liquid. The core assembly is carried in the tank and is removable after the separate closure is removed from the tank. The method contemplates separating the magnets from the tubes for removal of the magnetic particles from the magnetic core assembly externally of the tank and independently of the closure.