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Old 06-25-2017, 05:58 PM   #1
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Custom Black Water Tank

Looking to have a holding tank built to fit under the forward companion way and need recommendations on a quality manufacturer.

Thanks,
Don Sasser
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Old 06-25-2017, 06:13 PM   #2
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Your two best choices are either a 'plastic' tank (see link for one supplier) if they have a size that fits, or a custom FRP tank. You don't want to use any kind of metal, even if painted/coated. Black water is quite corrosive.

Boat Tanks | Marine Tanks - All Sizes (Water, Waste, Septic)
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Old 06-25-2017, 07:17 PM   #3
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Ronko Plastics makes quality tanks. I have bought several from them.
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Old 06-25-2017, 08:01 PM   #4
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I'll use Ronco Plastics to build the tank. Now one more question. Most diagrams shows the pumpout fitting in the end of the tank at the bottom . Would it not be better to have a fitting in the top of the tank with a drop tube going to the bottom of the tank?
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Old 06-25-2017, 08:54 PM   #5
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Ronco Plastics Ronco Plastics Marine Catalog (no relation to the VegoMatic Ronco) is your best source for a tank. Plastic Mart is a Ronco reseller...Ronco sells direct for considerably less. They make TOP quality thick-walled water and waste tanks for a very reasonable price and has 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--including discharge fittings on the top with pickup tube--when they make the tank. I'd also recommend that you specify a 1" vent.

Ronco only makes seamless rotomolded tanks..they can make a custom tank, but they'd have to build the mold, which would be very expensive. So in the unlikely event you can't find tank in the Ronco catalog that works for you, Triple M Plastics Triple M Plastic Products Inc would be your best source for a custom one-off tank.

Is this to be a replacement tank or a second tank for a second toilet? If you'd like to brainstorm a bit before ordering the tank and plumbing for it, feel free to send me a PM.
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Old 06-26-2017, 05:46 AM   #6
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Many of the boat assemblers in FL use these folks , Duracast.

A nice feature is they mark which tanks can go UPS rather than truck, which can save big bucks.

Duracast Products | DURACAST – ROTOMOLDING PLASTICS FOR ...


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Duracast, rotomolding, engineered rotomolding plastics products, molded plastic products, custom rotomolding plastics.
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Old 06-26-2017, 06:43 AM   #7
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Has anyone used a flexible tank? My boat came with a 40 gal built in fiberglass tank that must have leaked at some point, was cut out and replaced with a West Marine 20 gal. tank. I would like to have something larger, but have not pursued it farther than thinking about it.


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Old 06-26-2017, 07:31 AM   #8
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[QUOTE=Wmiii;567010]Has anyone used a flexible tank? My boat came with a 40 gal built in fiberglass tank that must have leaked at some point, was cut out and replaced with a West Marine 20 gal. tank. I would like to have something larger, but have not pursued it farther than thinking about it.


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I had a flexible black water tank on my boat. It started to smell after a couple of years. I replaced it with a rigid tank from Ronco.
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Old 06-26-2017, 08:00 AM   #9
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Quote:
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Your two best choices are either a 'plastic' tank (see link for one supplier) if they have a size that fits, or a custom FRP tank.

You don't want to use any kind of metal, even if painted/coated. Black water is quite corrosive.

This may be true but all the commercial (steel) shipyards I've spoken to all build boats with integrated steel black water tanks, with proper coatings. So from a practical point of view is it really not recommended to use steel?
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Old 06-26-2017, 08:13 AM   #10
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Many of the boat assemblers in FL use these folks , Duracast.
Duracast standard tank wall thickness is barely 1/4"...50% thinner than Ronco. You can order tanks with 3/8" walls from Duracast, but only for a huge upcharge in price.
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Old 06-26-2017, 08:35 AM   #11
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...but all the commercial (steel) shipyards I've spoken to all build boats with integrated steel black water tanks, with proper coatings. So from a practical point of view is it really not recommended to use steel?

Yes, unless you want a tank with walls at least 2" thick. The average lifespan of any metal tank--even 316 stainless--made for recreational boats is only about 10 years because urine is so corrosive that will first leak at a weld--a seam or a fitting within 2-5 years on average...while it's turning the tank into a colander.

Bladders aren't recommended either for several reasons: it's almost impossible to install it to prevent chafing, which results in leaks...they're highly prone to blow out fittings at the first sign of a blocked tank vent...and because they're designed to hug the contents, impossible to maintain aerobically, so impossible to prevent odor out the vent. And btw, USCG regs don't allow UNvented bladders to be used for waste holding because methane is flammable.
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Old 06-26-2017, 01:19 PM   #12
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As far as using a top pump out port with a pickup tube, the answer is yes you can. I have both my boats set up that way and it works fine.
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Old 06-26-2017, 01:52 PM   #13
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Ship engineers have figured out how to coat steel tanks well enough... otherwise there would be a clear alternative to integral tanks when you get into larger vessel size.

A thin walled plastic tank well supported in small boats or a steel tank with a good interior coating in large vessels sees no real difference in performance...both structurally sound and protected from the corrosive effects.

This has been beaten into me by marine engineers every time the topic comes up.
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Old 06-26-2017, 03:21 PM   #14
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I plan to install a Ronco tank with a bottom fitting for the drain.
I would think that a fitting in the top of the tank with a drop tube going to the bottom of the tank would not allow the tank to fully empty.
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Old 06-26-2017, 04:13 PM   #15
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I plan to install a Ronco tank with a bottom fitting for the drain. I would think that a fitting in the top of the tank with a drop tube going to the bottom of the tank would not allow the tank to fully empty.
That depends on the length of the pickup tube. If it's 1" off the bottom and cut flat across, it'll leave about the same amount as a fitting at the bottom of the tank. Shorter will leave more. If it's long enough to touch the bottom and cut at about 25 degree angle (less can trap undissolved solids or TP under it), it'll actually remove more than a fitting at the bottom.

Ship engineers have figured out how to coat steel tanks well enough... otherwise there would be a clear alternative to integral tanks when you get into larger vessel size.

If integral tanks on ships didn't have walls that are at least 3-5 x thicker than the 1/4"-3/8" that they are on recreational vessels, I have no doubt that there would be.
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Old 06-26-2017, 04:14 PM   #16
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Quote:
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I plan to install a Ronco tank with a bottom fitting for the drain.
I would think that a fitting in the top of the tank with a drop tube going to the bottom of the tank would not allow the tank to fully empty.
Also what I have thought too...

In fact, the best suggestions include a downturn in the hose after the outlet if possible so the tank drains into the hose. That way the macerator can keep pumping until tbe tank is empty to the bottom of that fitting.
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Old 06-26-2017, 11:54 PM   #17
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Best is Use the top mounted dip tube. The bit remaining will not be noticed I built my own tank of Nytex and epoxy but I built in a floor depression that the dip tube sat into with about 1" clearance so almost empties 100%.

If you insist on using the bottom port then install a shut off valve. Failure to do so will result in you getting bitten when the pump fails and the tank is full.
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Old 06-27-2017, 12:07 AM   #18
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If you use a bottom drain, be sure to install a valve there so you can work on the macerator pump while the tank is full. Raritan now makes a macerator pump with a built in valve.
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Old 06-27-2017, 01:30 AM   #19
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1/4" mild steel tanks can last a very long time if properly cared for. I maintained a boat with a 250 gal 1/4" mild steel black water tank for 34 years and that tank had quite a few years on it when we met. I left that boat 3 yrs ago and the tank still is in good condition. What is needed is full access to the exterior and interior to maintain the coatings.

In our recreational boats we want tanks tucked away in out of the way places, without large access hatches and we expect them to last decades un-maintained. For that we want heavy wall plastic tanks.

re top pick up vs bottom discharge. Top is the way to go. A leak or pipe / hose / valve failure is an annoyance with top pick up. It's a stinky, revolting disaster with bottom discharge. Very few things can rival a bilge full of black water to ruin your day.
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Old 06-27-2017, 06:04 AM   #20
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Bladders aren't recommended either for several reasons: it's almost impossible to install it to prevent chafing, which results in leaks...they're highly prone to blow out fittings at the first sign of a blocked tank vent...and because they're designed to hug the contents, impossible to maintain aerobically, so impossible to prevent odor out the vent. And btw, USCG regs don't allow UNvented bladders to be used for waste holding because methane is flammable.[/QUOTE]


Thank you , Peggy Hall, aka Headmistress. This is information that I needed.
I'll be looking to fit a larger solid tank in my space now.
Good information,

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