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Discussion Starter · #1 ·
So I am fitting a drain for my holding tank so I can dispose of our doo doo while offshore.

Which parts need to be below the water line to make sure I am not taking on seawater!
 

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West Marine has a very good schematic for designing a holding tank system. Look under west marine advisors.

You intake should have a valve and a vented loop before the head. You plumb the holding tank to a macerator and the through a valved thru-hull. You also need a vent and a hose that is T-ed to the hose to your macerator to deck for your pump out. That's your basic system.

Tod


Mandolin, Bayfield 36 sailing out of Rock Creek.

Sent from my iPhone using Tapatalk
 

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Right, I have the whole system already that has a pump out. I am trying to add a gravity drain to an existing thru-hull.
you mean a normal overboard drain right not GRAVITY drain...

no such thing if IM UNDERSTANDING right

do you already have a discharge thru hull or not?
 

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Discussion Starter · #5 ·
OK, so :)

The current set up is that I have a Y valve where I can direct to the holding tank, or have the head be discharged directly through a thru-hull. So, while offshore, I can poop overboard.

However, I now want to add the ability to drain the holding tank to go out through that overboard discharge thru-hull.

The scenario is that we have been anchored a few days and using the holding tank. Then we head out, there are no pump out stations around and I want to be able to drain the holding tank.....
 

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ok gotcha

just T it into the current discharge thru hull...you obviously cant loop it...it has to go down, in that same line however you have to have a valve to stop any water coming back in...

this is not a usual setup btw....what I always did was to add some soapy water or whatever through the pumpout drain on deck and then discharge whatever the hoding tank had to eliminate the smell

its almost impossible to manually drain all the doo doo by gravity...

unless you add a second pump
 

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Discussion Starter · #7 ·
just T it into the current discharge thru hull...you obviously cant loop it...it has to go down, in that same line however you have to have a valve to stop any water coming back in...
That's what I figured. I was just wondering if THAT valve needs to be below the waterline.
 

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the more I think about it the more I beleive no matter what the height of the tank is or what the distance of the thruhull is to the waterline that you are going to need a pump no matter what

a manual one is fine but basically you will have poop playing the up and down game in that line and quite possible youll have seawater getting into the tank...

my current boat has no holding tank its just straight thru
 

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im sure there are lots more people with better info on this...drwaings too on google images and the like

Im not completelt sure on what your best option is here...

honestly I would think its best NOT to add a drain for much the same reason fuel tanks dont allow it...if anything does happen and you get a leak or the drain breaks whatever you have poop IN the boat and bilges and that WOULD SUCK
 

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for what its worth most guys just discharge whatever they have after they are offshore and call it a day...not really minding if there are any "remnants" left

if you feel like you have to get it all out then add some freshwater and cleaner or whatever and "rinse" it out

good luck
 

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I've chartered boats (Bene's) that have gravity holding tanks (no macerator). The tanks are mounted high in the head in a cabinet (eye level). The head pumps directly to the holding tank. At the bottom of the holding tank is a large diameter hose to a thru hull.

I'm guessing they do it this way for cost reasons. To discharge directly overboard, leave the thru hull open. To hold waste, close it. When you're ready to dump waste overboard, open the valve. The boats I've seen this in have semi-transparent tanks so you can figure out how full by opening the cabinet (kinda gross).

All the boat's I've owned have had macerator pumps, anti-siphon loops, etc. as others have described.

I'm not expert in gravity systems but it would seem important that the tank is mounted high above the waterline, and the discharge hose/thru hull valve are large diameter. At least that's the way I've seen it done and it seems to work.
 

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By far the most efficient and trouble free holding tank system I've ever used was emptied by pressure. I would close all the incoming valves, open the 2" exhaust line and start an air compressor. As the pressure built up it pushed out the black water without any possibility of clogging. Air came in at the top, black water exited at the bottom. Simple.
 

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that to me sounds like the best...like a reverse pumpout version...

I can see where a gravity ONLY solution works great too but you already have a system installed so modding it might be overcomplicated

anywhoo
 
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