cwest wrote:
I suspect that I might have a heavy mineral build up in my holding tank.

It's possible that you have a sludge buildup, but it's not a mineral
buildup--not in the tank. Any sludge will be solids and TP that the use
of chemical tank products only allowed to dissolve into little tiny
particles that settled to the bottom instead of working WITH nature to
prevent odor while keeping the bacteria alive to emulsify (liquify) 'em.

If it's still "mud" it can be flushed out by putting a few gallons of
water down the pumpout hose--'cuz that sends the water into the tank at
the bottom to stir it up--pump that
out...repeat...repeat...repeat...till only clean water is being pumped out.

But if it's turned to "concrete," nothing will disssolve it that won't
also damage the tank.

Which is why it's VERY important to nominally rinse out the tank after
EVERY pumpout (sea water via a washdown hose after dumping a tank at sea
works)...and THOROUGHLY flush it out a couple of times a season. 'Cuz
left alone long enough, sludge will clog up a discharge hose and a
macerator.

I think I heard a while back that acetic acid (vinegar) works.

Nope. A cupful of white vinegar helps to prevent sea water calcium
carbonate buildup in the head discharge hose, but it won't do a thing
to dissolve sludge in a tank.

--
Peggie
----------
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://69.20.93.241/store/customer/p...40&cat=&page=1