getting rid of hard sediment in a black water tank.

[mestrezat]

Everything we've been getting out is small black chunks and chips. Put a stiff piece of old shroud wire up the discharge pipe and have been working it in and out. Standing upright,pouring water in the top and sloshing it around,some times tstuff comes out the bottom and sometimes not. Tilted on its side and lots more comes out the inlet. Repeated over and over. Shove the wire in the bottom outlet and pour in more water. Slowly coming cleaner as we keep doing it but have a ways to go. No sign of white calcium deposits, only black stuff. Not sure why sometimes liquid comes out the bottom and sometimes not. We have a way to go before satisfied. Will be tapping the sides today to break loose anything that's may be left..

[Dockhead]

Originally Posted by rwidman

Stainless steel is a poor choice for a holding tank and it's going to eventually start leaking. A pressure washer (preferably one that heats the water) would work. Detergents and a scraper should work but would be harder and take longer.

You could save some future problems by just replacing it now, not later, with a Polyethylene holding tank. There are several companies that make these in dozens of stock sizes. They are not expensive

I agree with this. Stainless holding tanks are nothing but trouble. With a site-fabricated tank, the problems will start with the welds. Sewage in the bilge is really unpleasant -- don't ask me how I know. I would replace now with a good plastic tank, if I were you.

[mestrezat]

When we bought the boat, the previous owner had it custom made and we being newbies had no clue. The water and diesel tanks are stainless so the black water tank should be to. Now, ten years late with the tank now 18 years old, it showing its age and believe me, I would replace it if I could but we're in Curaçao and getting a new plastic polyethylene tank is just not possible. I'm stuck with what I have till we get back to Mexico and finish the circumnavigation we started back in 2008. It just going to have to wait till them.

[CdS2 Roland]

Hello,
Most of the hard is calcareous you carry into your holding tank with urine.
So with stainless steel you can use phosfiric acid.


Remove before the most part and acid will do the rest.

[a64pilot]

Get a rubber mallet or rawhide and make some percussion adjustments.
That will likely knock it loose

[ranger58sb]

Originally Posted by thinwater

The key is knowing what the deposit is made of. If it is lime-like or scale-like, it is probably a combination of calcium salts, including hydroxide, phosphate, and urate.

The answer to these is acid, and not a very weak acid like vinegar. A complete waste of time. Also not muratic acid, since stainless does not like strong chloride under acid conditions. I would go for a descaling chemical like Barnicle Buster or Lime-Away. These will be 10-100 times faster than Vinegar and will take 10-20 times less. Let it soak, chip a little, and soak some more. It may take quite a lot.

We just had to solve a hard clog in our the discharge hose between toilet and waste tank. Apparently made up of uric acid crystals, or what Peggie often calls struvites, that turned solid after drying out for a few days (while I had the system open, working on an unrelated issue).

The same company that makes Barnacle Buster also makes a product called Sew Clean ("Soo" Clean). Raritan also private brands SC as C.H. (Cleans Hoses). I happened to have some BB concentrate on hand, and the MSDS says they're pretty much the same (a solution of phosphoric acid, with no info about concentration levels) so called the company to see if the stuff is interchangeable.

The answer was that BB just also contains some additional algaecides, but they projected BB wold work fine for our purpose. They instructed to use the SC dilution ration (5:1) instead of BB's 4:1, I think to extend the amount of usable concentrate. Soak overnight, flush. Repeat if necessary.

Using BB cleared the clog on the first soak. I repeated anyway.

Don't know if safe for stainless; didn't ask. Would assume it's dissolve that kind of sediment within a tank, though, not just in hoses.... assuming the sediment is on the bottom and lower sidewalls of the tank.

-Chris

[mestrezat]

Here's what we found today while working on cleaning all the sludge, etc out. I bought an aluminum rod to shove in the tank to break up what was left(along with a high pressure washer, auger, CLR(Calcium Lime and Rust cleaner) Septic tank cleaner) only to find out today as we took a flashlight and peered down the pump out tube that it's broken off about 5 inches down from the top! I've contacted a welder here in Curacao and will be taking the tank in for dismantling, cleaning and fixing on Wednesday. I think the "thunk" we keep hearing as we rocked the tank back and forth is the steel tube hitting the sides and bottom as it swings. Now why an I waiting two days, well just to make the "living the dream" that much better, I cracked a filling or maybe lost a filling in my teeth so I'm off to the dentist tomorrow. Man, this "Living the Dream" is expensive.
I'd love to put in a polyetheline tank but they just aren't available here in Curacao and importing one would double the cost. Once fixed, this baby should last me another five years or so when I can be a new tank and replace it properly.