Brian Whatcott wrote:
I have a thought. It's off the top, but it's worth testing.
Any acidic solution tends to eat metal.

Not necessarily. Vinegar is acid, but doesn't harm metal...chlorine
isn't acid, but is corrosive and does destroy metal.

Water doesn't even
need to be acidic to promote pin hole corrosion in some
aluminum alloys. Oxygen depleted water is hell on stainless.

But alkaline solutions, in general, don't eat metal so well, or at
all.

Urine can be alkaline or acidic...doesn't seem to matter in a metal
holding tank.

I have this hunch that waste water rendered slightly high pH
of neutral would help a tank to survive.

Waste and water have about the same pH...7-9...so I don't THINK pH is
the key...'cuz the same aluminum alloy tank used to hold water will last
20-25 years.

I'm not a chemist, so I can't tell you why that's true, only that it has
proven to be.

--
Peggie
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Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://shop.sailboatowners.com/boat_odors/