I hate to be the bearer of bad news, but any aluminum holding tank is living on borrowed time.
In the 1980s when holding tanks began to be required on boats, aluminum and steel were the materials of choice because they were less expensive and easier to cut and weld in odd shapes than rotationally molded polyethylene. But although you’ll still find aluminum or stainless holding tanks on some boats, by the early 1990s, it had become apparent that metal is a very bad choice for sewage holding because urine is one of the most corrosive materials it’s possible to put next to any metal and the industry began switching to plastic, most commonly LDPE (low density polyethylene).
While the sheet metal walls of a metal holding tank may last up to a decade (rarely any longer once it’s actually put in use to hold sewage), metal waste tanks, even 316 stainless steel, will typically begin to leak at a seam or a fitting within two to five years. You may be able to repair it, but the first leak is always just the first leak; urine is gradually turning the bottom of the tank into a colander. When this began to become apparent, a couple of aluminum tank mfrs began coating the inside of holding tanks with epoxy that extended holding tank life a few years. Stainless steel will last a little longer than aluminum, but even the best 316 stainless holding tanks rarely lasts more than 10 years no matter how diligent you are about pumping out and thoroughly rinsing out the tank every time you use the boat, never allowing waste to sit in it. Whether the toilet flushes with salt or fresh water makes no difference.
So it really doesn't matter what tank product is used in an aluminum holding tank, it's time to start preparing to replace it with a plastic tank. No-Flex Digestor does the best job of preventing odor, even in tanks that are insufficiently ventilated to function aerobically...any damage it might do to an aluminum tank is negligable compared to the damage urine is doing.
Btw... "Washing soda" (the common name for sodium percarbonate) is used for many household jobs and is the active ingredient in Oxyclean.
--Peggie
