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Old 24-07-2015, 13:14   #1
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Leaking fitting on polyethylene holding tank

The "weld" connecting the male threaded outlet on my holding tank has developed a significant leak. Is there a way to repair/reweld this fitting without having to pull the tank out of the boat?
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Old 24-07-2015, 13:35   #2
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Re: Leaking fitting on polyethylene holding tank

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Originally Posted by sowwaninii View Post
The "weld" connecting the male threaded outlet on my holding tank has developed a significant leak. Is there a way to repair/reweld this fitting without having to pull the tank out of the boat?
Just went through this. The welded connection is more likely a crack in the nylon through-hull fitting like one of these;


If it isn't, you can change it to one. I cut a hole in the top of the tank and put in an inspection plate so I could hold the inside mushroom while tightening the exterior nut. Kind of a sh!tty job but it has a better chance of long term success than a drop or crazy glue. Never hurts to have an inspection plate. Do a good job sealing it though.....


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Old 24-07-2015, 13:37   #3
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Re: Leaking fitting on polyethylene holding tank

If it's HDPE you can weld it, though getting the temperature right is tricky. There is lot's of HDPE around to practice on - milk bottles, garbage bags and lots of other stuff. Look at the recycling stamp on the bottom of any plastic container. I repaired a hole in my car's washer-fluid bottle using a ski-repair P-Tex stick. Took three tries, but the last one held. Or you could go and hire a professional - just don't tell him it's your holding tank until he's already on the boat and you've cast off your lines from the dock
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Old 24-07-2015, 13:39   #4
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Re: Leaking fitting on polyethylene holding tank

I like goat's solution better. Just FYI - if the tank is HDPE then no glue will stick. Including epoxy.
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Old 24-07-2015, 13:40   #5
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Re: Leaking fitting on polyethylene holding tank

Goat-
Thanks for the quick reply. I already have an inspection port so won't need to cut a new one. What did you use to seal the compression fitting, butyl tape?
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Old 24-07-2015, 13:47   #6
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Re: Leaking fitting on polyethylene holding tank

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Originally Posted by sowwaninii View Post
Goat-
Thanks for the quick reply. I already have an inspection port so won't need to cut a new one. What did you use to seal the compression fitting, butyl tape?
I used a 'tube' sealant but unfortunately brain abuse as a young man has effected memory somewhat now that I've got half a century under my belt. Butyl tape should work.

Good luck,

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Old 24-07-2015, 15:14   #7
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Re: Leaking fitting on polyethylene holding tank

There are now epoxies that will stick to HDPE. Gflex from West system will. They recommend flame treating the parts just prior to application. There are also now Loctite branded epoxies in the small double tubes available at hardware stores that claim to adhere to plastics that I suspect are similar formulations as the G flex. I have done a Gflex repair to a HDPE holding tank flange and it worked very well. I have also used it to repair an outboard motor fuel tank (also HDPE).
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Old 24-07-2015, 15:17   #8
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Re: Leaking fitting on polyethylene holding tank

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Originally Posted by goat View Post
Just went through this. The welded connection is more likely a crack in the nylon through-hull fitting like one of these;


If it isn't, you can change it to one. I cut a hole in the top of the tank and put in an inspection plate so I could hold the inside mushroom while tightening the exterior nut. Kind of a sh!tty job but it has a better chance of long term success than a drop or crazy glue. Never hurts to have an inspection plate. Do a good job sealing it though.....goat
There's a MUCH easier way. Thanks to a li'l doodad called the Uniseal UNISEAL you don't need access to the inside of the tank to move or replace a fitting on a plastic tank..ANY tank. They DO NOT LEAK. And a Uniseal is a tiny fraction of the price of a "fittings relocation kit."
See instructions for use here. Uniseal Instructions
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Old 24-07-2015, 15:24   #9
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Re: Leaking fitting on polyethylene holding tank

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Originally Posted by peghall View Post
There's a MUCH easier way. Thanks to a li'l doodad called the Uniseal UNISEAL you don't need access to the inside of the tank to move or replace a fitting on a plastic tank..ANY tank. They DO NOT LEAK. And a Uniseal is a tiny fraction of the price of a "fittings relocation kit."
See instructions for use here. Uniseal Instructions
There you have it. Take it from the pro. Thanks Peg, I've used your advice a lot over the years.

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Old 24-07-2015, 15:48   #10
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Re: Leaking fitting on polyethylene holding tank

Quote:
Originally Posted by peghall View Post
There's a MUCH easier way. Thanks to a li'l doodad called the Uniseal UNISEAL you don't need access to the inside of the tank to move or replace a fitting on a plastic tank..ANY tank. They DO NOT LEAK. And a Uniseal is a tiny fraction of the price of a "fittings relocation kit."
See instructions for use here. Uniseal Instructions
Read your book cover to cover, but guess I missed that chapter! THanks for the info. Alleviates much heart ache!
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Old 25-07-2015, 09:02   #11
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Re: Leaking fitting on polyethylene holding tank

I have had poly tank manufactures say try hot glue before anything for leaks in their tanks.

Worked for me on a RV water tank punctured by a wayward screw.
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Old 25-07-2015, 10:11   #12
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Re: Leaking fitting on polyethylene holding tank

The Uniseal that Peg posted about looks great but I suspect that it is only suitable if the area around the hole is the same circumference as the largest part of the Uniseal flange. It wouldn't work on my old vent outlet since it was at the very top edge of the tank. The seal would have kinked over at the top on the inside and have nothing to touch to on the upper top outer. If you have the room then you would have to cut a hole with a hole saw to remove the old fitting and the weld "bump".

Looks like the Uniseal would work but somehow I just like the physical security of a mechanical thread and nut seal. The advantage of the Uniseal looks to be not having to get your hand in to get a nut (or the fitting itself) on the inside of the tank. Which is what I had to do to put on a traditional bulkhead fitting for my new vent hole.
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Old 25-07-2015, 11:11   #13
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Re: Leaking fitting on polyethylene holding tank

You can weld it with a soldering iron and stick of donor plastic cut from something else made of the same type of plastic. If you don't have a soldering iron, I'm sure a screw driver heated with a propane torch would work, just heat the plastic up and stir it together, if the donor plastic is a different color, it's easy to tell when you have a good mix. You can use hole saws and relocate fittings this way, better if the plug can come from a different tank then you use a bigger hole saw to cut the fitting out and a slightly smaller one to cut out the hole it goes into, so there is not a really wide slot to fill that way, hole saws leave a wide kerf to fill. You might have to grind the edge of the plug to get a good tight fit before welding. Also remove the drill out of the center of the hole saw, and cut a dummy hole in a piece of wood that you use to center and locate the hole saw on the tank while cutting.
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Old 25-07-2015, 12:00   #14
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Re: Leaking fitting on polyethylene holding tank

Quote:
Originally Posted by peghall View Post
There's a MUCH easier way. Thanks to a li'l doodad called the Uniseal UNISEAL you don't need access to the inside of the tank to move or replace a fitting on a plastic tank..ANY tank. They DO NOT LEAK. And a Uniseal is a tiny fraction of the price of a "fittings relocation kit."
See instructions for use here. Uniseal Instructions
Amazing!
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Old 25-07-2015, 14:00   #15
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Re: Leaking fitting on polyethylene holding tank

Yes, Goats, reply good , I have done the same several years ago on another boat., I believe I got a kit from west marine that had everything to made the repair
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