getting rid of hard sediment in a black water tank.

[mestrezat]

My boat came with a stainless steel black water tank. We found out today that it's quite impacted with sediment, closing off the outlet to make the black water to the macerator. We have since removed the tank from it's place inside and took it on deck to try and get rid of the hard sediment with some success but it's still got a long way to go to be "clean".
Any suggestions on how to get rid of what's left? It's a mess!

[Bleemus]

Soak with a strong detergent and a lot of pressure washer work. If that fails you have to get to it with tools and chip it out.

[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

[mestrezat]

Last owner had it fabricated. Not in the US where I could get a new one easily. In Curaçao but thanks for,the input. Maybe once I get back to Mexico

[Dave22q]

You might try near boiling hot water with laundry detergent and lots of agitation. Another possibility is fill with fresh water and add a septic tank/RV type enzymatic cleaner to add **** eating bacteria. Good luck with this dirty job and I second the idea to replace with plastic ASAP.

[zeehag]

if you have access to odorlos, which is an enzyme, that works.
i tried the soap stuff, no joy. not workee. may have to uninstall it and clean it on the dock. oopsy. that blue stinky stuff also is fail.
ps plastic is easier to use and keep clean. can see the build up in bottom.

[Smokeys Kitchen]

And a third for not putting the stainless tank back in; it will just be a nightmare and probably at the wrong time.

Ronco Plastics most likely has one that fits your space. Look at their website. Get a hold of Peggy Hall on this forum for more info, she is the guru of marine waste systems.

[mestrezat]

Since what I have is stainless stell, is that a problem for,the septic cleaners?

[UNCIVILIZED]

Would vinegar work? It's a mild acid that's good at breaking down some other types of organic matter, & odds are it won't hurt the stainless. Might even try Coca Cola, it works in a similar fashion.
There are also ultrasonic cleaners, which work via vibrating things loose, & some are used along with vinegar, for a dual effect.

[wcapman]

I've had luck with 1 cup of gain laundry detergent and 1 cup of Calgon per 10 gals of tank size, diluted with 50% of the tank volume with VERY hot water and then agitated for awhile. I used an aquarium air pump and small hose to bubble air and keep the contents mildly agitated. Takes about a day to soften up, then repeat depending on how well it worked the first time. You can also try turning teh tank upside own and tapping on it with a rubber mallet.

[DrivinSteve]

Try loading it up with ice cubes and let them slosh around either by boat action or, if already out of the boat, strap it in a pickup truck and take it for a bumpy ride.
If not too thick, you might also try putting some ball bearings in and doing the same agitation. Make sure they are ferrous ball bearings so you can retrieve them with a magnet when done.

[Pete7]

Originally Posted by DrivinSteve

Make sure they are ferrous ball bearings so you can retrieve them with a magnet when done.

From inside a stainless steel tank?

Whilst the tank is out inspect very carefully every seem and edge because this is were its going to leak and it will eventually. When or if it goes back in the boat makes sure it can't move even a fraction because that is what will start the problems off.

Pete

[JeanneP]

In our 18 years living aboard our boat, our biggest problem was calcium deposits on all our water lines, containers, etc. At some point that calcium deposit is going to clog all drain lines in the boat, but the worst for calcium build-up was the salt-water outlet lines, and wastewater holding tank. We met a fellow who took all his clogged hoses out of the boat and beat them to break up the calcium.

I doubt that what is in your tank is organic build-up (though it is of course possible), but rather the calcium from the water precipitating it out.

Try this: just pour some full-strength vinegar in the tank (as in a quart or so), let it sit a an hour or two (or more), then hammer the bottom of the tank with something (NOT a hammer - something large-ish and without hard edges - pounding it with a soccer ball would probably work. Or, if it's still in the boat and can't come out, a wooden stick might work well.

if hard white-ish stuff (looks like plaster or broken dishes) comes loose, it's pretty certainly calcium. (stuff that oyster and clam shells are made of)

Rinse it out. More vinegar, repeat as needed. No soap, hot water, whatever, is going to work if it's calcium.

All our tanks on the boat were monel/stainless steel. 18 years, sailing from Boston to SE Asia (Singapore, Malaysia, Thailand). No leaks.

DO NOT USE ALUMINUM for any tankage. The slightest bit of copper debris (and there are lots of ways this finds it into your boat), and it will eat holes in the aluminum through electrolysis.

[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.

[ski69sail]

Hi There

You may need to cut hole in the top of your black water tank to truly get it clean. Then marine silicon a new plastic inspection hatch to the top. The water tight screw hatches that they use on kayaks will work well.
This may be the first time you clean your black/grey water tanks, but it will not be the last
Best of luck