Although a failed plastic holding tank was not Steve's problem, yes they can fail. I have a 40 gal plastic holding tank under the V-Berth. It almost conforms to the shape of the hull, with only an inch or so not touching along the bottom centre. A couple of years ago, with an almost full tank, we pounded for hours through high seas off the Nova Scotia coast. About five inches of the welded seam at the bottom of the tank let go. It allowed a very slow seep of black water, but only when the tank was over half full. I suspected the smell and slight staining was from a loose hose. Then one day, in another storm with an almost full tank, it failed further. Luckily it didn't rupture and I was able to quickly pump out and wipe up.
The tank is too big to remove from the V-Berth, so I cleaned it and turned it over for the repair. A Plastic Welder did the job in about an hour total. He even found and welded tiny cracks that spidered from the main failure. He tested it with 40 gal of fresh water and saw one slow drop start to seep from around the bottom fitting. He said that this happens as the fittings were not factory welded, but only spun into an undersize hole, melting themselves in place. We removed the tank and he welded around the bottom fitting. It held the 40 gal fine for twenty minutes while he put his tools away. The total cost in 2007 was $85.00, much cheaper and easier than a new tank.
I've installed shim supports to take the full weight of the tank and it works fine now. This may not be a problem with smaller tanks, but you have to make sure than a larger tank is well supported along it's full underside.
Cheers, Dana
The tank is too big to remove from the V-Berth, so I cleaned it and turned it over for the repair. A Plastic Welder did the job in about an hour total. He even found and welded tiny cracks that spidered from the main failure. He tested it with 40 gal of fresh water and saw one slow drop start to seep from around the bottom fitting. He said that this happens as the fittings were not factory welded, but only spun into an undersize hole, melting themselves in place. We removed the tank and he welded around the bottom fitting. It held the 40 gal fine for twenty minutes while he put his tools away. The total cost in 2007 was $85.00, much cheaper and easier than a new tank.
I've installed shim supports to take the full weight of the tank and it works fine now. This may not be a problem with smaller tanks, but you have to make sure than a larger tank is well supported along it's full underside.
Cheers, Dana