The glass bowl filters were popular to visually check contamination and water, many were equipped with a petcock to drain off the water. In some applications they may be OK, maybe in a vintage application, but I would recommend its replacement with a finer filter/water separator in a marine application. If you cannot or wish not to pull the tank, then possibly Brandon's recommendation is notable. There are many products available to clean, and then coat the tank before re-use, but you must pull the tank to do this. Given the condition of the current filter, I'd say there is likely some rust/contamination in the tank. If it were me, I'd add a simple in-line metal filter at the tank, then a marine filter/separator at the engine so that its weight is not stressing the tanks fitting.