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Old 05-22-2017, 08:08 AM   #1
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Black Water Tank Replace or Repair?

I have a 1984 Grand Banks Classic with a crappy problem. Some black water in my bilge leads me to believe I have a leak in the metal (carbon steel I think) black water tank. Sides and bottom are not visible so location of crack or pinhole(s) not identifiable. I pumped out the tank and my immediate plan is to remove the square plate on top, roughly 6" x 6", that also serves hose connections and see if it's possible to clean inside entirely and locate point of leak. Would like to know of anyone who has gone through this already and get tips on what to do and not to do. Is it a waste of time to clean out tank, instead just replace it? What is best material choice for a new black water tank, fiberglass or AL or steel? Tank supplier names? Is an epoxy repair of old tank possible?
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Old 05-22-2017, 08:24 AM   #2
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Replace the tank. I wouldn't even try to repair it. Our last boat (1981 year) had a steel tank. When I pulled it out, I rinsed it and looked inside. Yikes!! It had a lot of pitting and more than 1/2 dozen pin holes.
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Old 05-22-2017, 08:40 AM   #3
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Black Water Tank - Repair or Replace

Thanks Larry!
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Old 05-22-2017, 08:45 AM   #4
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My boat has a fiberglass tank nearly 30 years old with a gel coated interior.


last time I had it open, I rinsed it off and with very little effort cleaned it...looked like you could eat off the walls.


Plastic is my second choice.
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Old 05-22-2017, 08:46 AM   #5
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No question, replace. Black water is not something to try and get away with. A failure of the tank could ruin any trip and probably some weeks after.
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Old 05-22-2017, 08:46 AM   #6
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Replace it

I too wouldn't even think of repairing it. Replace it with a polyethylene tank. Perhaps the best supplier is Ronco Plastics (Ronco Plastics - Marine Water Tanks, RV Water Tank, Auto Detail Tanks, Water Tanks). They will make you a custom tank to fit your spot.
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Old 05-22-2017, 08:51 AM   #7
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Replace it. Metal tanks for black water are problematic because of the acidic contents. Use a poly tank.
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Old 05-22-2017, 09:02 AM   #8
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You've gotten good advice: replace it! 'Cuz urine is so corrosive that the first leak in a metal waste tank is only the FIRST leak....it's turning your tank into a colander.

Ronco Plastics Ronco Plastics Marine Catalog (no relation to the VegoMatic Ronco) is your best source for a tank. They make TOP quality thick-walled water and waste 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.
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Old 05-22-2017, 09:25 AM   #9
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Black Water Tank Replace or Repair

Thanks all for great advice! Jesse and Good Vibrations.
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Old 07-20-2017, 05:09 PM   #10
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Do any of you have experience removing a holding tank from a Grand Banks 42 Classic? The guys I brought in to do the job removed all 2x2 wood hold downs around tank perimeter and at corners. The tank won't budge. It's only 10% full. Seems to be bonded at the bottom somehow. Shouldn't it just lift right out?
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Old 07-20-2017, 05:26 PM   #11
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I suspect that waste leaking out of the bottom of it has "glued" it down, 'cuz you're right...it should just lift out. Hopefully they haven't already removed all the hoses, 'cuz you REALLY need to pump that remaining 10% out of the tank and rinse it out as thoroughly as possible so that what's likely to spill out the bottom when they pry it loose is just water...at least mostly water anyway.

If they have removed all the hoses, replace the pumpout line if you can. Or maybe (I'm admittedly reaching a bit here) cut a hole in the top big enough to stick the dock pumpout hose or ANY pump hose down into to get it all.
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Old 07-20-2017, 07:05 PM   #12
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Holding Tank Stuck

Headmistress, thanks so much for reply. That does sound like a possible cause. Also, since you appear to have much expertise on this - would you suspect my 60" long holding tank is baffled? Reason why is the company I hired has recommended I allow them to cut the top of the old tank with a sawzall, thoroughly clean the inside of the tank out, leave the old tank shell bottom and sides in the boat and install the slightly smaller new plastic Ronco tank inside the old tank shell. Do you see that as an acceptable solution? Of course if tank is not baffled, this would be easy to do but baffling may make this solution impractical.
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Old 07-20-2017, 09:43 PM   #13
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Rotomolded plastic tanks are rarely if ever baffled, but it's not unusual for welded metal or plastic to be baffled. However, whether yours is or not is immaterial because unless you want to have to deal with a whole new set of problems created by a rusting hunk of scrap metal wrapped around a top quality plastic tank, that entire tank must come out.

They're telling you they can cut the top off and completely clean the tank...that might possible if it were a fuel or water tank, but urine turns metal holding tanks into colanders. When they start trying to clean it, parts of the bottom and sides will crumble. When that starts to happen, they may try patches...for all of which you'd be paying 'em several times what it'll cost you just to get the d'd out of the boat. Yes, there'll prob'ly be a spill...but it'll actually be easy--and a LOT less expensive!--to successfully clean and permanently deodorize that area...I'll be glad to walk you through it. In fact for less than half of what I'm sure that company wants to charge you to leave that tank in place, I'll come to Houston and supervise the removal and clean up for you...it's that easy.
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Old 07-20-2017, 11:21 PM   #14
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And when it still stinks and you get rust coming out from under the old tank in a year or two, is this contractor going to come and fix the problems?
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Old 07-21-2017, 03:37 AM   #15
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You can have them suck the contents out with a Shop Vac without removing the entire top. It took me a few trips to the marina head to empty the Shop Vac, but much easier than cutting off the top of the tank.
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