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Old 13-11-2016, 15:12   #1
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Blackwater Holding Tanks

The blackwater holding tank on my boat is clogged and none of the commercially available chemicals appear to work. I have flushed the system through and this cleared a lot of calcium deposits. Has anyone tried using hydrochloric acid? In theory the acid will attack the lime/calcium deposits but will it cause harm to the system? The tank is stainless steel with a heavy plastic hose to a morelon Forespar seacock.
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Old 13-11-2016, 18:04   #2
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Re: Blackwater Holding Tanks

"The tank is clogged" can mean a lot of things...can you be more specific? Specifically what is clogged? What specifically makes you think it is?

I need a lot more details to know what to recommend.
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Old 13-11-2016, 23:26   #3
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Re: Blackwater Holding Tanks

Thanks for the reply. I disconnected the pipe leading from the bottom of the holding tank to the seacock and nothing came out of the full tank. I pumped the tank out with a manual pump and tried cleaning it from inside (through the deck) and through the exit pipe with a hose. A lot of caked very hard lime came out (a disgusting task) into the bilge. Now the tank does drain through the seacock but only slowly. I thought that acid could be used to dissolve the lime concretions.
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Old 14-11-2016, 01:36   #4
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Re: Blackwater Holding Tanks

Don't use acids they will corrode your stainless steel tank!
You need an alkaline cleaner, you should be able to get a commercial kitchen cleaner or descaler from cafe or kitchen supply store, It is also used for cleaning coffee machines and milk or brewery vats
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Old 14-11-2016, 07:38   #5
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Re: Blackwater Holding Tanks

There is a product that's sold in OZ that will dissolve the buildup safely: NoFlex Digestor Noflex Digestor, It's getting rave reviews in the US and Canada. Scroll down and read the instructions for use in recreational marine holding tanks.

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Old 14-11-2016, 07:55   #6
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Re: Blackwater Holding Tanks

i have used and carry Drano liquid in my spares. It never let me down
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Old 14-11-2016, 07:57   #7
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Re: Blackwater Holding Tanks

Actually hydrochloric acid (aka muriatic acid) is safe to use in a sanitation system...it's one of the most popular ways to dissolve sea water mineral buildup in hoses.

But his problem isn't only scale...it's also urine crystals ("struvites"...google the term to find quite a bit on it in wikipedia)...acids formulated to dissolve scale won't dissolve urine crystals.

However, he'll have another problem if he doesn't already: his tank is steel. Urine is so corrosive that it typically turns ANY metal tank into a colander in an average of about 10 years. The first leaks usually occur in a weld--a seam or a fitting--within 2-5 years. That's the time to start researching sources for plastic tanks--most commonly seamless rotomolded polyethylene--because that first leak is always only the FIRST leak. By the time you have to patch it, the bottom is already pitted.

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Old 14-11-2016, 08:27   #8
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Re: Blackwater Holding Tanks

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i have used and carry Drano liquid in my spares. It never let me down
NEVER use any household chemical bowl cleaners, drain openers, pine oil cleaners, bleach or anything that contains bleach in a marine sanitation system. They're ok for household use because household plumbing is hard pvc and household toilets have no rubber parts (except in the flush water tank).

However, most of the plumbing on most boats involves rubber...and if you read the MSDS for Drano, you'll see the ingredients in it are highly corrosive and destructive to rubber--the rubber parts in toilets and it breaks down hose resistance to odor permeation. Drano Liquid Drain Cleaner MSDS | MsdsDigital.com | Search our SDS online database free | Material Safety Data Sheet (It's an awkward version, but the only one I could find that IS a link instead of just a downloadable PDF)

You won't need a drain opener if you flush a cupful of distilled white vinegar all the way through the system once a week...follow after about 45 minutes with a couple of quarts of clean fresh water. Vinegar isn't practical as a drain OPENER (although a combination of vinegar and baking soda is an amazing "clog buster")...but it does a great job of PREVENTING sea water mineral buildup in hoses. And prevention is always easier and usually a lot cheaper than cure!

Btw, I see you're FL...I'll be at the St. Pete boat show next month, scheduled to give 5 seminars. The rest of the time I'll be hanging out an area called the "authors corner." Would love to meet you if you're planning to come to the show.

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Old 14-11-2016, 08:48   #9
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Re: Blackwater Holding Tanks

Quote:
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Urine is so corrosive that it typically turns ANY metal tank into a colander in an average of about 10 years. The first leaks usually occur in a weld--a seam or a fitting--within 2-5 years. Peggie
Peggie - Have passed 10 years without a leak in my custom built stainless holding tank. The holding tank is attached to a Sealand Vacuflush head which means even less dilution of the waste. So, a far more concentrated blend in the tank. We'll see how long it lasts.

I used stainless in order to maximize the available tank volume. A plastic tank just didn't work in my application.
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Old 14-11-2016, 13:30   #10
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Re: Blackwater Holding Tanks

Note that I did say "typically," "usually" and "average"...some last longer, some don't last that long.

A shame you didn't know where to look for custom plastic tanks, 'cuz Triple M Plastics in Maine Triple M Plastic Products Inc could have made you a top quality plastic tank exactly the same dimensions and capacity as your steel tank. When that one does fail, they're your best source for a replacement.

Low flush water volume results in an increased concentration of urine crystal to build up in your tank. I suggest that you also consider regular applications of No-Flex Noflex Digestor
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Old 14-11-2016, 13:43   #11
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Re: Blackwater Holding Tanks

The oxide layer that protects stainless is easily damaged. Stagnant chloride solutions are to be avoided.

Might be simpler to cut an access panel, mechanically clean, pickle the cleaned stainless. This is the quickest and most effective approach.

Aggressive acidic solutions are a poor choice for other than a simple cleaning. Hot caustic would work but its probably simpler to mechanically clean.

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Old 14-11-2016, 13:45   #12
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Re: Blackwater Holding Tanks

On a quick side note.

I'm fitting 2 tanks in my boat to replace one bladder and the other just emptys overboard.

When I empty the tanks, should I part fill them with some sea water rather than leave them empty.

Should I empty and part fill then empty again to flush them out a bit more?

The boat came with some powder he said to put a teaspoon in each time you empty. Is this because it's a bladder or will the rigid tanks want this too.
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Old 14-11-2016, 14:38   #13
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Re: Blackwater Holding Tanks

Quote:
Originally Posted by peghall View Post
You won't need a drain opener if you flush a cupful of distilled white vinegar all the way through the system once a week...follow after about 45 minutes with a couple of quarts of clean fresh water. Vinegar isn't practical as a drain OPENER (although a combination of vinegar and baking soda is an amazing "clog buster")...but it does a great job of PREVENTING sea water mineral buildup in hoses. And prevention is always easier and usually a lot cheaper than cure! http://www.amazon.com/New-Get-Rid-Bo...dp/1892399784/
And a video to prove it:

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Old 14-11-2016, 14:40   #14
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Re: Blackwater Holding Tanks

Pump or dump the tank, then at least nominally rinse it...sea water if fine.

Since I have no idea what the powder is, I can't tell you what it's supposed to do. However, I can tell you that there are no tank products just specifically for bladders only, so it would be for use in either or both tanks.

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Old 14-11-2016, 16:46   #15
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Re: Blackwater Holding Tanks

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Originally Posted by peghall View Post
Note that I did say "typically," "usually" and "average"...some last longer, some don't last that long.

A shame you didn't know where to look for custom plastic tanks, 'cuz Triple M Plastics in Maine Triple M Plastic Products Inc could have made you a top quality plastic tank exactly the same dimensions and capacity as your steel tank. When that one does fail, they're your best source for a replacement.

Low flush water volume results in an increased concentration of urine crystal to build up in your tank. I suggest that you also consider regular applications of No-Flex Noflex Digestor
First thanks for the tip on the custom plastic tank company. I missed them 10 years ago.

Second, low flush water volume will probably not result in an increased concentration of urine crystal in my tank. The flush water is fresh up here in Lake Superior.

Lastly, I got an A in reading comprehension, thanks. Was letting you know that on a sample of 1 my tank is a factor of 2 outside your norms. It could fail in the next year or it could keep going forever. We will see.
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