Black Water Holding Tank Replacement / Repair

[L!fe48]

Hello,

This looks like a great forum. This is my first post and I appreciate all feedback.

I have a 2000 48' Wendon Cockpit Motoryacht with two heads and Vacuflush system that feed into one aluminum 80-gallon black holding tank. The tank seems to be leaking when about 25-gallons full. I suspect it is a seam but no way to diagnose that.

I would like to replace that tank but that may be "impossible," at the very least an extremely large job. It would include draining two fuel tanks and removing all plumbing associated with them as well as other systems that are in front of the tank. Once that is done, I suspect it will require carpentry work in the master stateroom to remove the tank.

In the image, the tank is on the bottom and extends forward (under the top panel) another 16" or so. On the backside of the top panel is a built-in set of drawers in the master stateroom that are over top of the tank.

Please let me know if there are any other suggestions for sealing the tank from the inside. I can cut an 8" access hole from the front of the tank.

Thank you in advance. Smooth sailing to all!

 

[READY]

Welcome.
This will not be very helpful but I believe there are companies who can coat the interior of tanks. Maybe try a goggle search?

 

[Mac2]

I just had a conversation with Peggy (HeadMistress on this forum and the ultimate informational source on everything holding tank) about your exact issue. I have a steel holding tank (several hundred gallons) and she advised me how urine will eat away a metal tank if it is not coated heavily on the inside. She said it will usually start at a weld. One suggestion (if this ever happened to me) would be to cut the top off and glue the plastic holding tank material to the interior of my existing tank (I only have about 10 inches of clearance above my tank). It looks like you have great access and could have a custom holding tank installed after cutting the top of your existing tank off. I suppose it will depend on what it looks like inside. I would be curious to know what material is sprayed inside a tank that would resist urine.

 

[Hobbit]

Our tanks have been epoxy barrier coated, we have very good access to them thru a 24" diameter bolted on hatch. They are all aluminum and look like new inside, no sign of any corrosion. This was all done by a previous experienced owner who new what he was doing.

 

[SIBERNUT]

I am told there is an "Aircraft slushing compound " that will seal pinhole type leaks in a tank. An alternative might be to eat less Mexican......

 

[Mac2]

I am told there is an "Aircraft slushing compound " that will seal pinhole type leaks in a tank. An alternative might be to eat less Mexican......

Has anyone heard of “black tar epoxy “?

 

[Comodave]

Welcome aboard. It may be painful but I would replace the tank with one from Ronco. They make a quality heavy duty plastic tank. They will install all the fittings in the locations you specify. As said above you don’t want a metal tank for holding the head discharge. If it has one leak now it will get more in the future.

 

[HeadMistress]

Dave is right...the first leak in a metal holding tank is ONLY the FIRST leak. What none of you seem to realize is that while epoxy can delay leaks in metal tanks, it'll prevent 'em for only so long. There was--maybe still is--an aluminum tank mfr in FL named Florida Marine Tanks that coated the insides of 'em with epoxy...lifespans of their holding tanks was about the same as uncoated tanks. Leaks in welds can be sealed using JB Weld (I once knew a houseboat owner he'd done that so many times, he wasn't far from having an entire tank made of JB Weld!) Meanhile urine has been busy turning the bottom of the tank into a colander. Just as new hoses are the only permanent cure for permeated hoses, a new plastic tank is the only permanent cure for a leaking metal tank--any metal tank, even 316 stainless.

Ronco Plastics is my go-to water and holding tank mfr because they build TOP quality thick walled (50% thicker than "off the shelf" holding tanks for a very reasonable price, install fittings in the sizes and locations specified by the customer when they make the tank and have 400+ shapes and sizes in their catalog that can be oriented in any direction because there is no top or bottom until the fittings are installed and you decide where they go, often eliminating the need to pay the price for a custom tank.

Ronco Plastics Water and Waste Holding Tanks catalog
Ronco Plastics marine Tank drawings

--Peggie

 

[Comodave]

My knowledge about holding tanks and all things poop related comes from Peggie. Credit goes to her, thanks Peggie.

 

[HopCar]

I agree with Dave and Peggy - Ronco. They make about 500 sizes and shapes of tanks.

If you don’t want to do that, these guys can make a flexible tank liner for you. Fuel Bladders | Custom Lightweight Boat Fuel Tanks | Aero Tec Laboratories

 

[HeadMistress]

Flexible ("bladder") tanks are ok for fuel and water, but not for waste because they hug the contents, leaving no air space that allows the tank to breathe. And, fwiw, it's not necessary to vent water tanks, but USCG regs require that all waste tanks (fuel tanks too) be vented to the outside of the boat...pretty much guaranteeing that the air flushed out of a bladder tank vent with every flush will STINK!

--Peggie

 

[Comodave]

And I think I might rather have a fuel tank leak than a holding tank…

 

[receptionraritaneng]

Hello,

This looks like a great forum. This is my first post and I appreciate all feedback.

I have a 2000 48' Wendon Cockpit Motoryacht with two heads and Vacuflush system that feed into one aluminum 80-gallon black holding tank. The tank seems to be leaking when about 25-gallons full. I suspect it is a seam but no way to diagnose that.

I would like to replace that tank but that may be "impossible," at the very least an extremely large job. It would include draining two fuel tanks and removing all plumbing associated with them as well as other systems that are in front of the tank. Once that is done, I suspect it will require carpentry work in the master stateroom to remove the tank.

In the image, the tank is on the bottom and extends forward (under the top panel) another 16" or so. On the backside of the top panel is a built-in set of drawers in the master stateroom that are over top of the tank.

Please let me know if there are any other suggestions for sealing the tank from the inside. I can cut an 8" access hole from the front of the tank.

Thank you in advance. Smooth sailing to all!View attachment 156979

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