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Old 20-01-2022, 09:55   #1
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Best way to decommission an inaccessible holding tank?

Hi all,

My new-to-me boat has a standard marine head which I want to rip out and replace with a composting head (as on my old boat).

Unfortunately the holding tank is built under the front sole and is pretty inaccessible - what's the best way to decommission it? Do I flush it a lot and hope for the best?

The hoses are pretty gross so would also like to remove them all as well (well, as much as I can)
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Old 20-01-2022, 10:37   #2
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Re: Best way to decommission an inaccessible holding tank?

Flush with a bleach solution. Bleach destroys lipids, and cell walls are made of lipids, so no carbon-based life form survives bleach. Good stuff, used appropriately. Once you've flushed the dead stuff, cut the hoses as close to the tank as possible, plug, and clamp the plugs in place. Remember that it has a vent.
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Old 20-01-2022, 11:47   #3
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Re: Best way to decommission an inaccessible holding tank?

Step 1. Flush GALLONS of clean fresh water through the system

Step 2. Fill and pump or dump the holding tank several times, adding the water to it via the deck pumpout fitting 'cuz that sends it into the tank at the bottom to stir up any sludge and hold it in suspension so it can removed. Add bleach if you want to....prob'ly should if the tank will remain in place.

Removing hoses
Start with the highest connections, duct tape the ends as you remove each one.

Warming the old hoses a bit (I always used a blow dryer) will make them easier to get off the fittings.

Put a plastic waste basket liner under each connection to catch any spills.

Since you won't be re-using the tank, seal the female tank fittings with threaded plugs wrapped in plenty of teflon tape. That will prevent odors from the inside of the tank from escaping.

--Peggie
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Old 20-01-2022, 12:31   #4
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Re: Best way to decommission an inaccessible holding tank?

Quote:
Originally Posted by peghall View Post
Step 1. Flush GALLONS of clean fresh water through the system

Step 2. Fill and pump or dump the holding tank several times, adding the water to it via the deck pumpout fitting 'cuz that sends it into the tank at the bottom to stir up any sludge and hold it in suspension so it can removed. Add bleach if you want to....prob'ly should if the tank will remain in place.

Removing hoses
Start with the highest connections, duct tape the ends as you remove each one.

Warming the old hoses a bit (I always used a blow dryer) will make them easier to get off the fittings.

Put a plastic waste basket liner under each connection to catch any spills.

Since you won't be re-using the tank, seal the female tank fittings with threaded plugs wrapped in plenty of teflon tape. That will prevent odors from the inside of the tank from escaping.

--Peggie
Should the vent remain in place or should it also be removed and plugged?
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Old 20-01-2022, 15:32   #5
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Re: Best way to decommission an inaccessible holding tank?

Agree with all the above but you need a scouring detergent like TIDE POWDER then go out and sail the boat and slosh it around. Pump out and repeat a FEW TIMES. You'll never get I clean unless you "scour it" that way. I did this a few times and then decommissioned re hoses etc. Never been an issue since and Yes I left the vents INTACT.
Not positive but I think this was a Peggy Hall suggestion I might be in error there.
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Old 20-01-2022, 17:25   #6
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Re: Best way to decommission an inaccessible holding tank?

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Should the vent remain in place or should it also be removed and plugged?
Plug it ALL.
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Old 20-01-2022, 18:35   #7
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Re: Best way to decommission an inaccessible holding tank?

This issue has come up before. Pasted in below are our prior comments:

"My two cents is that you may want considering plumbing your liquids tank to the holding tank, instead of dumping the liquids tank fairly often (depending on how much you use the head).

We live aboard our boat all summer at a mooring in a crowded harbor. Dumping the liquids tank overboard may or may not be illegal, but is, at the very least, rude to ones neighbors. Hence, we plumbed our Airhead liquids tank directly to our holding tank and vented the composter thru a small mushroom vent in the head. We like this arrangement for we only have to pump out the holding tank liquids every three weeks.

Just a thought. We're not the first composter owners who have done this.

Cheers, and enjoy the new composter. Once you get the hang of using it, you'll never want to go back to a conventional head with its finicky plumbing."
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Old 20-01-2022, 18:46   #8
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Re: Best way to decommission an inaccessible holding tank?

That's a good question. He said the tank is pretty much inaccessible, so I can't see any harm in leaving the vent line in place unless that tank fitting happens to be accessible. It won't take long for dust, pollen and critters to clog up the vent thru-hull, so no need to do anything to it.

--Peggie
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Old 20-01-2022, 18:57   #9
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Re: Best way to decommission an inaccessible holding tank?

What Peggie said. I had good success using expanding foam to seal off my hoses. I have a 37 yo boat that had the hoses running aft to forward about 24 feet. Quite the project to get them out as they dip down and were filled with
..but I drilled a hole in the top of the hose each end or where i was cutting and filled with a 1/4 can of gap filling foam. Easily cut foam filled hose with a Sawzall and no mess. Practice first to get a feel for how much you need. Remember sewage can be fun...not.
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Old 20-01-2022, 23:49   #10
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Re: Best way to decommission an inaccessible holding tank?

Unless the boat will be scrapped when you are done with her, you may want to consider making your changes reversable in case a future owner may want to go back to a typical head arrangement.
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Old 21-01-2022, 00:18   #11
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Re: Best way to decommission an inaccessible holding tank?

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Unless the boat will be scrapped when you are done with her, you may want to consider making your changes reversable in case a future owner may want to go back to a typical head arrangement.
Indeed. If I was looking at at a boat with a composting head I would need to calculate how much it would cost me to install a real toilet.
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Old 21-01-2022, 01:52   #12
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Re: Best way to decommission an inaccessible holding tank?

Thanks for the advice all, some great stuff here that is really useful.

Re: using the holding tanks for liquids, I've heard of some people doing that who liked it but I'd prefer to get the hoses out of the way entirely, the simplicity of compositors are one of the reasons I like them so much.

Re: reversable for selling - not bothered about that. My old boat sold really fast for asking and that had the holding tank physically removed when I put in the composter so it doesn't seem to affect resell value much. I don't think anyone who looked at the boat even mentioned it. If someone was dead set on it they could always add a new tank in somewhere else I guess
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