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Old 16-10-2009, 02:47   #1
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What Size Holding Tank? (Merged)

Sorry if the answers in here some where but so far can't find it, even with a Google search. What I notice is that a lot of waste holding tanks on the market and in boats seem very small and would like some advice on this and system installation.

What I have is a compact Jabsco manual pump toilet going directly outboard. Happy to keep this because it fits and I have learnt how to maintain it. The boat has an integral fibreglass tank never connected. It would be relatively easy to do so but I don't want to. I don't like the position and don't trust the fibreglass build for holding waste over time. So will probably install a poly tank somewhere and have read on this forum lots of good advice about how I might do this - but nothing about how big this tank should be.

Some vital statstics - 38ft sail boat epoxy/cedar construction. Usually two to three on board for extended periods, including areas with no pump out facilities and no-discharge zones.
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Old 16-10-2009, 04:03   #2
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It's not the size of the...

I have a deepening suspicion that it's not the size of the holding tank that matters, but the effectiveness of the gauge that measures how full it is.

Don't ask how I know what a black deposit inside a boat is...
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Old 16-10-2009, 04:17   #3
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Is there a diet variable that has to be factored in? ?;-)
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Old 16-10-2009, 05:49   #4
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20 gallons seems to be a good size. I wouldn't go much bigger and maybe only a little smaller. Think about it. Do you really want to haul a LOT of waste around? This stuff does not improve with age. When it fills up you need to empty it. You can generally empty it in most places that sell fuel. So you need enough capacity to get you covered between stops. If you go out in the open water frequently then a macerator and and Y valve so you can dump it would be worth while too.
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Old 16-10-2009, 06:16   #5
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Definitly worth getting hold of Amazon.com: Get Rid of Boat Odors: A Boat Owners Guide to Marine Sanitation Systems and Other Sources of Aggravation and Odor (9781892399151): Peggie Hall: Books This is Peggy Hall's book on marine toilets, and she knows more about this subject than most people. (aka the Headmistress)

When we last corresponded, she recommended consideration of a Class 1 MSD as an alternative to the holding tank. An additional battery to power it is a lot smaller than a holding tank.
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Old 16-10-2009, 06:26   #6
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I don't carry it about when I don't need to, but I want the freedom of cruising without pump out anxieties. We're two aboard with fulltime East Coast US cruising on a 41' and I find 40 gallons ideal even though I rarely fill it.
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Old 16-10-2009, 06:37   #7
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Quote:
Originally Posted by GypsyHawk View Post
will probably install a poly tank somewhere and have read on this forum lots of good advice about how I might do this .
Quote from a very knowledgeable expert in this area

"Sailboats especially are often fitted with flexible tanks--also known as bladders. We recommend against their use for sewage holding (but not necessarily for water or diesel) as well. Bladders are invariably installed in an area of the boat thatís inaccessible to install a rigid tankóstuffed down any opening into a place big enough to contain it. And only rarely are the bladders properly secured to prevent any movement. Since sailboats are typically so much more "active" than houseboats or cruisers, heeling side to side, bladders move and chafe till they leak. Fittings must be owner-installed, and because the tank is in an inaccessible place, it is almost impossible to install the fittings correctly. Rarely, if ever, is any holding tank checked or maintained, and especially since some arenít even vented, it isnít at all uncommon for a bladder to blow out its fittings. Furthermore (for reasons Iíll explain later), it is all but impossible to control odor in a flexible tank. The very qualities that make bladders attractive to install make them undesirable for use for sewage holding."
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Old 16-10-2009, 06:49   #8
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We use an MSD I but with fresh water and a Chloride injector. It uses far less power than the salt water versions.

Our last boat had a bladder. It worked well and lasted about 18 years. Eventually the bladder permeated just like the hoses. It was well secured under the V Berth. I wouldn't say it was a perfect solution but they do work. You can order poly tanks cutom made really really cheap over the internet. They can do any dmensions and make the ports where you want them. All tanks require a good secure mounting. A 40 gallon tank full is going to weigh more then 320 lbs.. You don't want that getting loose or have even a small wiggle.
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Old 16-10-2009, 07:03   #9
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Mount your new tank if you can above the waterline with a short hose and valve to a throughhull.
Open valve and dump, no need for a macerater pump and all of its problems.
Install a short hose for a deck fill directly above the tank so flushing out with a bucket of sea water is easy.
A 15-20 gal tank is all one needs, promotes dumping and pumping out. Two people produce about 5 gal of waste in 2-3 days.
If a preformed tank will not fit build one of fiberglass, line it with expoxy.
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Old 16-10-2009, 08:31   #10
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LOL. What marvelous topics we discuss with such relish!

2 people, 5 gals, 2-3 days sounds about right for people who flush sensibly. A little longer if you can discharge clean yellow fluids (may require 2*WC, etc). Your needs depend on factors like POB, time spent in one spot, local regs, and attitudes to discharging near other boats.

So 20 gals would cover Susan and I for over a week. Given we move every day or so (bar major storms), and don't have to leave the 12 mile limit to discharge, we get by on less. Costs & time taken to install small vs. large storage systems do not differ greatly. If you have the space you may as well double what you think you need.
When I do discharge, I am very concious of other water users. Many cruisers have saltwater taps, and viral particles concentrate in the sediment until wave action brings them up as a dense suspension.
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Old 16-10-2009, 08:49   #11
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We have a 25 gallon bladder, which has served quite well for the past 15 years. It fills up in about 6 days if we reserve it for the poop. Definitely have a way to pump it overboard as well as the deck pumpout fitting, because you can't depend on pumpout stations.
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Old 16-10-2009, 09:21   #12
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...... A 40 gallon tank full is going to weigh more then 320 lbs.. You don't want that getting loose or have even a small wiggle.
Excellent advice here, but please note my suggestion for the 40 gallon tank was to have the ability for the volume not the typical use. I rarely have my tank over half full, but then I never have to adjust my cruising plans to search for a pump out. For that important security of the tank I made use of the nylon tie down straps that hold towed boats to their trailers secured to eye-bolts in addition to a confining frame. Since my boat was built before holding tanks were standard I added my tank to an area that formerly held a 75 gallon water tank. I still carry 200 gallons of water. Admittedly the 320 pounds would be harsh, but I'm normally just carrying 15lbs of extra tank for my assurance. It's probabky important to factor in how you use your boat as well. We are fulltime year 'round cruising. 'take care and joy, Aythya crew
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Old 16-10-2009, 10:21   #13
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30 gal. for a 38' boat.
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Old 16-10-2009, 10:23   #14
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Whatever you get it will not be big enough and if you are in out of the way places you will need to just dump it between harbors while you are under way. Much of the time it's just a temporary holding vessel to make you "legal" and keep from polluting the anchorage. I've always liked the Hallberg Rassy approach: tank above waterline, all head waste goes into tank, short hose and seacock at the bottom, open the valve underway and it gravity feeds out. Nothing to breakdown....
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Old 16-10-2009, 17:16   #15
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Cheech - the thing I don't like about that design, is that you can't choose to put the pee overboard - everything goes in the tank, and you can't selectively send the pee overboard. I prefer to have a Y valve before the tank. I do like the idea of having the tank above waterline though. Mine is installed with a lavac, so I can use the henderson pump to pump out the tank, when out beyond the limit.
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