It has nothing to do with salt water....the culprit is urine. It's so corrosive that ANY metal tank, even 316 stainless will typically start to leak at a weld--a seam or a fitting within 2-5 years, and turn into a colander in an average of 10 years. And it doesn't make any difference how often the tank is pumped and rinsed, or what tank products are used in it. Although aluminum was originally the most popular choice among builders, by the early 90s seamless rotomolded polyethylene had become the only recommended material for waste holding.
So it's entirely possible your hoses are the source of the odor now...or both could be culprits. But even if the tank isn't leaking yet, it will...and the first leak is always only the FIRST leak. So the smartest thing you can do is replace it now.
Meanwhile, test your hoses for permeation...put a clean rag in HOT water...wring it out and wrap it around a section of hose. When the rag has cooled, remove it and smell it. If you can't smell anything on it, that hose hasn't permeated...if you can, it has. The only cure for permeated hose is new hose.
The easiest way to find a leak in the tank: fill it with water to which you've added a bottle of red food coloring. In 24 hours you'll see a red wet spot where any leak is.
The best source for a replacement is Ronco Plastics (no relation to the VegOmatic Ronco)...they make TOP quality thick walled plastic tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular...and they install fittings in the sizes and locations specified by the customer when they make the tank, eliminating any need for "fitting relocation kits." They've been suppliers to most of the high end boat builders for several decades. And they also sell direct. Their tank catalog is here:
Ronco Plastics Marine Catalog
(Thanks for the plug, Parks!)