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Old 08-28-2015, 06:39 PM   #1
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Salt water flush and AL holding tanks

I've read that some aluminum holding tanks will fail if you have a salt water flush system. Something about the urine and the salt water reacting?

I have this setup, and a slight sewage smell near the tank. Thought it might be hoses but then read this.

True? False?
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Old 08-28-2015, 11:09 PM   #2
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Hi Cardude, aluminum is about the worst possible material for a holding tank. I don't think it matters if you flush with fresh or salt, black water is corrosive.

That said, there could be other sources of the odor. Take a clean cotton cloth, dampen it with warm water and wipe it over your sanitation hoses. Smell the rag. If the rag smells bad replace the hoses.

Another source of toilet odor in salt water is that aquatic flora and fauna get trapped in the rim of the toilet bowl and rot. This one fools a lot of people as they keep looking for problems on the discharge side of the toilet.

Unfortunately pin holes in an aluminum tank are a real possibility.

Get ahold of Peggie Hall's book on controlling boat odors. She really knows her sh*t.
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Old 08-28-2015, 11:28 PM   #3
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It has nothing to do with salt water....the culprit is urine. It's so corrosive that ANY metal tank, even 316 stainless will typically start to leak at a weld--a seam or a fitting within 2-5 years, and turn into a colander in an average of 10 years. And it doesn't make any difference how often the tank is pumped and rinsed, or what tank products are used in it. Although aluminum was originally the most popular choice among builders, by the early 90s seamless rotomolded polyethylene had become the only recommended material for waste holding.

So it's entirely possible your hoses are the source of the odor now...or both could be culprits. But even if the tank isn't leaking yet, it will...and the first leak is always only the FIRST leak. So the smartest thing you can do is replace it now.

Meanwhile, test your hoses for permeation...put a clean rag in HOT water...wring it out and wrap it around a section of hose. When the rag has cooled, remove it and smell it. If you can't smell anything on it, that hose hasn't permeated...if you can, it has. The only cure for permeated hose is new hose.

The easiest way to find a leak in the tank: fill it with water to which you've added a bottle of red food coloring. In 24 hours you'll see a red wet spot where any leak is.

The best source for a replacement is Ronco Plastics (no relation to the VegOmatic Ronco)...they make TOP quality thick walled plastic tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular...and they install fittings in the sizes and locations specified by the customer when they make the tank, eliminating any need for "fitting relocation kits." They've been suppliers to most of the high end boat builders for several decades. And they also sell direct. Their tank catalog is here: Ronco Plastics Marine Catalog

(Thanks for the plug, Parks!)
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Old 08-29-2015, 08:11 AM   #4
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Cardude, a little off subject but how did you come out on your transmission issue?
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Old 08-29-2015, 08:14 AM   #5
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We have all sorts of chemicals to keep waste tanks from stinking.

NO ONE has worked out what chemical to drop into an aluminum tank to keep it from dissolving?

I smell a profit center here!
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Old 08-29-2015, 08:21 AM   #6
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Seawater will have little negative impact on a marine aluminum alloy. Blackwater may be alkaline or acidic (pH between 6 and 8.5) and usually tends to the alkaline which is not great for aluminum.

In real life, the problem with using aluminum for wastewater tanks on small boats is that they tend to be made of very thin, uncoated material. The problem is not so much the material as the thickness and method of fabrication. Large aluminum boats use integral waste tanks but they are made of thicker material and coated with high solids epoxy or other polymers that result in a long and satisfactory life.

Stainless steel is arguably the worst material, particularly if relatively thin and uncoated. The oxygen poor environment in a holding tank is lethal to uncoated stainless steel. Even when coated, the smallest crack formed by wall flexing or lack of backing gas when welded will provide a place for a corrosion cell to start tunneling to the outside.

Poor welding quality only accelerates the process. Unless you are willing to pay for a high quality tank fabrication, plastic tanks like those described above are the best solution for most recreational boaters.
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Old 08-29-2015, 08:52 AM   #7
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Yikes. Replacing that tank is not something I look forward to doing. It is forward under the master, and seems to be encapsulated in fiberglass for some reason. Sigh.

Is there any way to adjust the PH of the waste water, like a pool? Make it more acidic?

I recently cleaned out the HT vent and the smell in the boat seems to be better, but I can still smell it around the tank and hoses.

Will do the hose test next.

Thanks for all the help as usual!
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Old 08-29-2015, 10:10 AM   #8
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Aluminum tank

When I bought my boat it had a 200 gal aluminum holding tank. When I installed my Electroscan system I removed the twenty year old tank and replaced it with a roto molded 100 gallon and used the extra space for my new equipment. The tank to my surprize was coated with epoxy and showed no corrosion. I had to cut up the tank to remove it. It was 1/4 inch aluminum welded plate. So I guess if properly coated aluminum will hold up.
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Old 08-29-2015, 11:14 AM   #9
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Once again Peggy's information is great! Thank you. Replacing any part or the whole system is money well spent when it comes to holding tanks, you will be way "a head" of the game in the long run by doing it right. We installed new tanks, hoses and heads in our boat and have no issues whatsoever. No smell no leaks and everything done correctly. Read Peggy's book, it is a great resource.

It does require a fair amount of labor to change out the tanks and hoses but it is doable.
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Old 08-29-2015, 11:31 AM   #10
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Quote:
It has nothing to do with salt water....the culprit is urine. It's so corrosive that ANY metal tank, even 316 stainless will typically start to leak at a weld--a seam or a fitting within 2-5 years, and turn into a colander in an average of 10 years.
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Once again Peggy's information is great!

Great If you don't mind rash generalizations "ANY metal tank ...will typically ... turn into a colander ..." based on lack of information or experience with the subject material.

That is opinion and mythology, not information.

And, as usual, subsequent posts by actual users countered the mythology and fear mongering.
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Old 08-29-2015, 08:06 PM   #11
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Not sure where the mythology and fear mongering is coming from but our old tanks were aluminum and leaking before we removed them and replaced them with plastic.

My experience is limited to this install but I followed Peggy's book and recommendations and everything has worked flawlessly for two seasons now.

I would begin with the hose checking as suggested and the dye to check for any leaks to have more info to work with.
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Old 08-29-2015, 09:30 PM   #12
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Great If you don't mind rash generalizations "ANY metal tank ...will typically ... turn into a colander ..." based on lack of information or experience with the subject material.That is opinion and mythology, not information. And, as usual, subsequent posts by actual users countered the mythology and fear mongering.
The marine sanitation industry had enough widespread information and experience with metal waste tanks by 1990 to recommend seamless rotomolded PE as the preferred tank material for waste tanks. If you want to tell the experts that their recommendations are based on "mythology and generalization" and "rash generalizations" it's ok with me. But I'm gonna continue to call things as THEY see 'em.
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Old 08-29-2015, 10:09 PM   #13
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Who is the marine sanitation industry?

What is curious is how a 2008 Island Packer wound up with an aluminum holding tank.

Pretty notable builder using something that should have been long gone by then.
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Old 08-29-2015, 10:28 PM   #14
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Unlike CG regs, standards are not compulsory...and old habits have a way dying hard.
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Old 08-29-2015, 10:53 PM   #15
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Who is the marine sanitation industry?

What is curious is how a 2008 Island Packer wound up with an aluminum holding tank.

Pretty notable builder using something that should have been long gone by then.
Very good point. Frankly, I would have expected IP to install the latest stuff. Surely the plastic plus installation couldn't have cost more. Of course, I suppose they could have had a pile of alum tanks out back, but duh?!
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Old 08-30-2015, 07:48 AM   #16
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Very good point. Frankly, I would have expected IP to install the latest stuff. Surely the plastic plus installation couldn't have cost more. Of course, I suppose they could have had a pile of alum tanks out back, but duh?!
Based on Scary's post of au recreational example and Rick's where obviously large vessels use integral tanks...I thought I would read further.

I was suprised to see so many metal tank fabricators advertising aluminum or stainless holding tanks.

They posted all the USCG, ABYC, NMMA logos and listed how they met all the regs or guidelines.

It is often mentioned in marine articles how plastic has taken over the market but doesn't seem to be all that clearcut...like in cardude's case or certainly Rick's that like many thinks in boating, there is more than one way to do something if done correctly.
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Old 08-30-2015, 10:28 AM   #17
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My boat is aluminum... 5086 series alloy specifically. All tankage is integral to the hull, so basically my boat is a giant aluminum tank. 1500 gallons diesel, 800 gallons fresh water, and 400 gallons black water. There is also a 60 gallon non-integral grey water tank/sump.

The boat was built in 1992 and has had fresh water flush the entire life of the vessel. The 400 gallon blackwater holding tank has no leaks and no signs of corrosion. There is a large "man hole" inspection plate. I'm sure some day there will be repair or replacement necessary. Nothing is forever, but 23 years and going strong isn't too shabby.
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Old 08-30-2015, 10:51 AM   #18
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Salt water flush and AL holding tanks

I sent an email to the IP rep who has answered questions for me before, asking if the SP and PY black tanks are possibly epoxy coated or something.

Will post up when I hear from him.

I find it hard to believe that IP would install a tank that will only last 10 years, especially after all the holding tank problems some of their older model boats have had.
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Old 08-30-2015, 11:11 AM   #19
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Recommendations are not mandates. And any container that receives and retains sewage but does not discharge it is automatically USCG certified as a Type III MSD.. I knew houseboat owners on Lake Lanier in GA who bought recycled CocaCola syrup barrels to use as holding tanks that also met all USCG, ABYC, NMMA regs or guidelines. That didn't make 'em a good choice, nor does the fact that aluminum waste tanks claiming--accurately--that they also meet all USCG, ABYC, NMMA regs or guidelines are being offered for sale mean that they're a good choice.

You "gentlemen" can continue to beat this--and me--to death if you want to...but I have better things to do.
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Old 08-30-2015, 11:27 AM   #20
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Recommendations are not mandates. And any container that receives and retains sewage but does not discharge it is automatically USCG certified as a Type III MSD.. I knew houseboat owners on Lake Lanier in GA who bought recycled CocaCola syrup barrels to use as holding tanks that also met all USCG, ABYC, NMMA regs or guidelines. That didn't make 'em a good choice, nor does the fact that aluminum waste tanks claiming--accurately--that they also meet all USCG, ABYC, NMMA regs or guidelines are being offered for sale mean that they're a good choice.

You "gentlemen" can continue to beat this--and me--to death if you want to...but I have better things to do.
Peggy, I for one really apreciate your insite, knowledge and participation. Regardless of what a very few people seem to indicate, you are the foremost expert on marine sanitation, and your advice is very much apreciated and listened to by the vast majority of the membership here.
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