You can...muriatic (hydrochloric) acid has been the accepted de-scaler for marine
piping and sanitation systems for decades because it does the job without harm to anything in the system including toilets, and it's also safe to use in a metal tank. In fact, it's what Raritan
recommended for cleaning
out the Lectra/San till they decided to add a ready-to-use descaler to their sanitation and cleaning products line.
However, descaling is the ONLY thing that muriatic acid does...and in 25 years I've yet to see a holding tank that has enough mineral buildup in it to need it.
Dirty tank walls are coated with the animal fats in waste, not scale...a strong solution of liquid detergent (Wisk is good...a couple of gallons) in a tank full of water
with a bag full of ice cubes is all you need to cure that problem...go sailing and tack a lot. Then flush VERY thoroughly with clean water.
Sludge, unless it's been allowed to dry and turn to "concrete" can be flushed out with just water (directions to follow)...but if it has turned to concrete, NOTHING will dissolve it that won't damage the system...you're stuck with it. But I've yet to see enough buildup in a tank to block the discharge or make a noticeable difference in the capacity.
The following should be done 2-3x/year, and especially in preparation for winter or other extended layup
out the tank, or dump it at sea. Then put enough water into the tank via the deck
pumpout--'cuz that sends the water into the tank at the bottom to stir up the sludge and hold it in suspension so it can be pumped out--to cover the bottom to a depth
of 4-6"...it can be fresh water at the dock
or sea water using a washdown pump. Pump out or dump...repeat...repeat...repeat...till you're pumping or dumping clean water. Then one last time to rinse out any macerator and plumbing
And while you have the hose in your hand, backflush the tank vent too.
If you're doing this in preparation for winter layup
or extended storage
, this should be done with clean FRESH water and also run through any macerator overboard
to rinse them out too.
And with that, my friends, I bid you a fond farewell. Email
me if you need help.