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Old 15-09-2019, 18:49   #1
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Leaking plastic freshwater tank at drain

This is actually on my motorhome but I was referred to this site. My first post.

This is a 3/4" threaded drain that had a 3/4" threaded male to slip adapter screwed in with a drain pipe to a drain valve. After 24 years it cracked.

I'm calling the factory tomorrow to find out what type of plastic tank this is and ideas on how to fix it.

In the meantime what do you all think I should do to repair this? The work area is real tight. Not much room. This is a view looking up from the ground in my back. The crack is that dark line. The tank cannot be removed.

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Old 15-09-2019, 18:56   #2
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Re: Leaking plastic freshwater tank at drain

Can you get a hose clamp around the flange to hold it together and bed the male part in with sealant? Not ideal but it might tide you over for a while.
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Old 15-09-2019, 19:10   #3
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Re: Leaking plastic freshwater tank at drain

Get a bulkhead fitting such as from BANJO. Cut out the failed nipple and replace with a bulkhead fitting.

Bulkhead Fittings/Tank Accessories
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Old 15-09-2019, 19:17   #4
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Re: Leaking plastic freshwater tank at drain

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Originally Posted by DefinitelyMe View Post
Can you get a hose clamp around the flange to hold it together and bed the male part in with sealant? Not ideal but it might tide you over for a while.
I got a clamp around it for this failed try.
Zoom in and notice the two "bumps" that prevent uniform pressure when tightening.

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Old 15-09-2019, 19:21   #5
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Re: Leaking plastic freshwater tank at drain

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Originally Posted by Nicholson58 View Post
Get a bulkhead fitting such as from BANJO. Cut out the failed nipple and replace with a bulkhead fitting.

Bulkhead Fittings/Tank Accessories
Thank you but there is no way to get into the tank to secure for tightening a bulkhead fitting.
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Old 15-09-2019, 19:33   #6
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Re: Leaking plastic freshwater tank at drain

Have you tried screwing in a brass plug with lots and lots of goop on it? That plumbers paste stuff?

I had a similar problem. In my RV. The exact same tank fitting. Mine was rubbing against a crossmember and it cracked. I was able to thread in a threaded brass plug from Home Depot. And I loaded it up with the plumbers paste. It’s been good for like a year and a half now. And a lot of really really bumpy roads. I ride with the water tank completely full also.

Maybe give that a shot instead of the rubber plug that you are using. Because it doesn’t make enough Contact with everything in that tank fitting.

Worst case, if the plumbers paste doesn’t work, you could take some epoxy and do exactly what I was saying. Just epoxy up that whole thing... All the threads... and screw the brass threaded plug in. That should do it.
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Old 15-09-2019, 19:35   #7
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Re: Leaking plastic freshwater tank at drain

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Thank you but there is no way to get into the tank to secure for tightening a bulkhead fitting.
You need an inspection port. Can you add one? Otherwise look for after market replacements. Lots of tank makers furnish tanks for boat and RV makers. It might just be a standard unit.

Most plastic tanks are polyethylene. No glue will stick. Ports are added by a skilled guy with a plastic welder.
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Old 16-09-2019, 05:33   #8
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Re: Leaking plastic freshwater tank at drain

No need to call the factory to find out what the tank is made of...it's polyethylene. Unfortunately there is no sealant or "glue" that can bond permanently to PE...fittings must be installed using a process called "spin welding" that melts the edge of the fitting and the edge of the hole it's going into so that they run together to become a continuous mass. Since it's unlikely the fitting can be replaced without removing the tank, I'm afraid that's what you'll have to do.



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Old 16-09-2019, 06:06   #9
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Re: Leaking plastic freshwater tank at drain

Look into Locktite 3035. Apparently is is an adhesive for PE. It is being used to repair PE kayaks, apparently with success. You may need to be creative to come up with a repair strategy after reading about it.
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Old 16-09-2019, 06:44   #10
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Re: Leaking plastic freshwater tank at drain

While looking for a polyethylene adhesive I found this:

https://www.permabond.com/2015/03/31...-polyethylene/
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Old 16-09-2019, 06:49   #11
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Re: Leaking plastic freshwater tank at drain

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Look into Locktite 3035. Apparently is is an adhesive for PE. It is being used to repair PE kayaks, apparently with success. You may need to be creative to come up with a repair strategy after reading about it.
Thank you I will check it out.
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Old 16-09-2019, 07:07   #12
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Re: Leaking plastic freshwater tank at drain

I just did, and then sent an email to the company. If Loctite 3035 actually does bond permanently to PE--a bond strong enough to withstand the stress of a male NPT standard threaded fitting in a female threaded fitting--it's the first thing that can and badly needed! I'm looking forward to their reply!


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Old 16-09-2019, 07:43   #13
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Re: Leaking plastic freshwater tank at drain

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I just did, and then sent an email to the company. If Loctite 3035 actually does bond permanently to PE--a bond strong enough to withstand the stress of a male NPT standard threaded fitting in a female threaded fitting--it's the first thing that can and badly needed! I'm looking forward to their reply!


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If this adhesive works I'm wondering if I should notch that crack to allow the adhesive to bond it together better?
There isn't enough room for a hacksaw blade but a thin hot knife maybe?
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Old 16-09-2019, 09:02   #14
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Re: Leaking plastic freshwater tank at drain

I have been told on another forum that G-Flex 655 works on PE. You must first use some heat on the repair area. I have not tried it on my tank so can't confirm.

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Old 16-09-2019, 09:52   #15
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Re: Leaking plastic freshwater tank at drain

Don't do anything until I hear back from Loctite...their contact form said to expect a reply within 72 hours, so it may be a couple of days.



Meanwhile...heat welding requires a tool that can melt both sides of the crack while it injects new material. That's prob'ly gonna screw up the threads. If there's a plastics fabricator in you area, you might want to give them a call to find out what you can do to salvage it. If there is one, and IF you can remove the tank, it's a simple matter for them to remove the cracked fitting and spinweld a new one into the tank.


I'll get back to y'all as soon as I know more.


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