Dometic 28gal. blackwater holding tank leaking from threaded insert

Danny Troy

Danny Troy

Member
Oct 8, 2009
861
Candlewood Lake, CT
Boat Info
2003 280 Sundancer
Engines
496MAG w/genset
I finally took my holding tank out today and found that one of the 4 threaded inserts, located on the bottom at each of the 4 corners, is leaking. They all look a little rusty, but only one is leaking. Funny, they aren't even used, as the tank is held down by the fittings on the outer bottom of the 4 sides of the tank. Any idea of how to fix this leak? I plan to call Dometic/Sealand tomorrow, but thought I'd post here, hoping someone had the same problem. The model number is HTS28. I have a hot air plastic welder and will be picking up a pack of HDPE welding sticks tomorrow. I don't know of any othe r way to fix the tank, other than plastic welding it. A new tank is $800.00, which is way more than I'd like to spend on a new tank. tank_leak.jpg
 
Nice to know I'm not alone with this problem. I'm calling the manufacturer tomorrow and see what they say. They obviously screwed up big time with this design flaw. Maybe by now they have a repair kit, or at least can recommend a permanent solution. I'm thinking about heating the insert and pulling it out, and welding in new HDPE. If I go that route I'll try the leaking fitting first, to see if it holds. I'm lucky, in that I was able to get the tank out, and have it at my home to work on it. Of course, it's outside, since it wreaks!!!
 
sdleo26 said:
I been there, see below for fix, going on 3rd season and still holding

http://clubsearay.com/showpost.php?p=689854
Click to expand...

BTW, did you happen to see exactly where it was leaking from? Was the leak at the center of the metal fitting, or was it from the outer part, where it seals with the plastic? If it is the center, I can see where JB Weld would probably work.
 
Danny Troy said:
BTW, did you happen to see exactly where it was leaking from? Was the leak at the center of the metal fitting, or was it from the outer part, where it seals with the plastic? If it is the center, I can see where JB Weld would probably work.
Click to expand...

From what I recall, it was more in the area of the metal hardware versus the seal of the part/plastic. Seeing that you have the tank out of the boat, you are obviously in an better position to try something more permanent (i.e., plastic weld). I am interested to see what you get out of Dometic when you call. They were of no use when I called two years ago. They were adamant that there was no hardware that protruded through the tank, but obviously we all beg to differ.
 
OK, called Dometic. They weren't completely useless, since they advised me on how to do the repair. He asked me if I wanted a new tank, and for a half a second I thought he was giving me one gratis. He offered to do the repair for $300.00 and I would have to take it to him on Long Island. The repair they do is to leave the metal fittings in place, fill the hole with HDPE and basically cover the entire area with new HDPE, using a plastic welder. He also said they put on little feet, surrounding the repair. So, I went ahead and made the same exact repair. The total cost was $43.00 for the plastic welder from Harbor Freight, $16.00 for enough HDPE welding rods to last 2 lifetimes, and $15.00 for the soldering iron type plastic welder, also from HF. I used that to smooth out the work while the HDPE was still molten. I had that plastic welder already, so the total repair only cost $58.00, and I get to keep the tools. I also saved a few hours driving and tolls, not having to take it to Dometic for the repair.

Right now it sits half full of water on a dolly on my driveway, and so far not a drop.
 
I wanted the one with the built-in air source, but it wasn't in stock, so I got the type that uses your compressor for air. Probably better off with that one anyway, since I won't have to worry about the built-in air pump crapping out. At $42.00 or so, it's a good tool to have. The $15.00 unit is a pretty good also, but it never could have done this repair alone. Harbor Freight to the rescue, again!
 
Good to know... What is HDPE? If mine starts leaking again, perhaps you can share procedure??
 
High Density Polyethylene. I think what most plastic tanks (and even milk containers), are made from. Not a hard procedure with the hot air plastic welder. There are some videos on YouTube describing the process.

Look at the bottom of most any piece of plastic and you will find a triangle, with letters signifying what type plastic it is. The thing about plastic welding, is that you must use the same exact type plastic welding rod as the material you are welding. Here's some of the symbols:

recycle1.gif
PETE
recycle2.gif
HDPE - high density polyethylene
recycle3.gif
PVC - polyvinyl chloride
recycle4.gif
LDPE - low density polyethylene
recycle5.gif
PP - polypropylene
recycle6.gif
PS - polystyrene
recycle7.gif
Resins not mentioned above, or a combination of plastics.
 
Thanks to everyone posting regarding this topic.

For anyone with a 300 Sundancer from 2002 to 2007, I just worked with a friend of mine to remove the holding tank. I thought that I would have to remove the outer riser of the port engine, but my buddy figured out a way to remove the tank by removing the head pump and lowering the fresh water manifold (with all the blue and red hoses attached).

Also, there are 6 mounting screws/inserts, 4 of which have to be removed, and the 2 towards the stern of the bilge (when facing the tank they are the ones on the left side of the tank) are VERY hard to remove. The 2 that at the port bulkhead of the bilge can remain in place. There are brass inserts that allow the tank to slide out. I had seen many posts stating that there were only 2 in front that had to be removed. I just wanted to warn anyone doing this job that those 2 screws/inserts on the left side of the tank are the hardest part of the job.

I have yet to finish the job, but just wanted to share this just in case anyone was thinking about attempting this job this season. To me, the greatest victory was not having to remove the elbow and riser of the port engine. I'm sure that it's not hard to do, but I don't like disturbing things that are not having issues.

Btw, to remove the screws it helps to have a 10 in and 6 in extender for your ratchet.

Hope this helps future holding tank repairs.

Eddie
703-626-7625
 
I misspoke in the number of screws/inserts - there are 8, 6 of which use be removed. All but the rear 2 screws/inserts towards the port bulkhead
 
Ok,

I was right the first time. 4 of 6 screws. My buddy had told me there were 8. He did all the hard labor. The 2 screws that are to remove DO NOT have to be removed, just as everyone said, but I thought the back of the tank meant the screws towards the bulkhead, but actually they are the ones toward the stern of the boat, or if you're facing the tank, they're on the left side of the tank.

I've wanted to attach pictures of the finished plastic welds, but haven't figured it out.
 
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