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Old 09-29-2016, 11:04 AM   #1
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Odd holding tank configuration

I just spent 5 days onboard a sailboat with a holding tank configuration that struck me as odd. The boat is part of a membership club and on loan to the school I teach at so it isn't mine to worry about or change. Rather than a Y valve, the head output goes to a T fitting with a seacock on one side and a holding tank on the other. The holding tank is about 1.5' higher than the seat of the head so I guess the waste goes through the seacock as long as it is open, but the hoses would always be full of waste below the height of the tank when the seacock is closed. (It is always left closed due to the boat's location) This configuration seems like a really dumb idea. It appeared to be the stock configuration from a reputable builder. Has anyone else seen anything like this?
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Old 09-29-2016, 11:54 AM   #2
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Installing the tank entirely above the waterline allows it to be dumped using gravity. In most installations, everything goes into the tank...or through it if the seacock is open. The idea is to keep it simple...no y-valves or pumps. There are a couple of drawbacks to it.... If the dry mode on a manual toilet isn't used long enough to move the flush all the way to the tank, what doesn't make it can run back to the toilet...and sludge can pack the discharge hose from the tank if the thru-hull stays closed most of the time. That may be reason they opted for tee with a second line to the thru-hull...however, it would have made more sense just to put enough water into the tank to rinse the bottom and flush out the discharge line on a regular basis.

This configuration seems like a really dumb idea.
If this boat can't ever get out to sea far enough to send sewage overboard, it is a dumb idea.

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Old 09-30-2016, 10:18 AM   #3
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When we chartered a sailboat from Marmaris, Turkey, all of the charter boats in our group(fleet of 10) had a similar setup. Unfortunately, the tanks were tiny, so discharge had to occur at least every second day. There were no pumpouts available, so all these small discharges went overboard, into the crystal clear water of the Med.
The gravity discharge worked very well, but when one of our group allowed their tank to fill right up, discharge was, by default, directed out the vent. Don't be standing on the dock when one of these boats is side tied!
Shouts of "Stop pumping, NOW".
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Old 09-30-2016, 10:31 AM   #4
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I would be willing to wager this one is probably plugged with sediment from the T down to the seacock due to lack of exercise but I honestly didn't consider that this configuration would allow a gravity flow dumping and it was certainly well above the waterline. It is amusing to me that recreational vessels receive such scrutiny in my area yet heavy rain events overwhelm the treatment plants and dump millions of gallons of untreated sewage into our Bay.
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Old 09-30-2016, 10:53 AM   #5
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My friend's sailboat(46ft) has the head seawater inlet below sea level. The system relies totally on the user closing the inlet valve after use, and no leaking/failure of that valve. On more than a few occasions guests leaving the valve open have allowed the toilet to overflow. Seems to me like an accident waiting to happen but I guess sailboaters are kind of seat of the pants guys!!!
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Old 09-30-2016, 12:20 PM   #6
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Quote:
Originally Posted by Chrisjs View Post
My friend's sailboat(46ft) has the head seawater inlet below sea level. The system relies totally on the user closing the inlet valve after use, and no leaking/failure of that valve. On more than a few occasions guests leaving the valve open have allowed the toilet to overflow. Seems to me like an accident waiting to happen but I guess sailboaters are kind of seat of the pants guys!!!
It is an accident waiting to happen...if his toilet is left in the "wet" mode when no one is aboard to notice that their feet are getting wet in the cabin, his boat can sink in its slip.

Your friend he (or whoever installed his toilet, which could have been the builder) should have read the installation instructions...and it's not only sailors who don't think they need to. The installation instructions for every seawater toilet--manual and electric--make it very clear, and even include drawings, that ALL seawater toilets with even part of the bowl below waterline MUST have a vented loop in the intake that's at least 6-8" above waterline at ANY angle of heel...which on most sailboats puts it 3-4 FEET above the bowl. Power boats don't heel much, so 8-10" inches above waterline when the boat is at rest with full tanks (200-300 gallons of fuel and water can raise the waterline several inches) is high enough.

On a manual toilet and any electric toilet that has a short hose connecting the pump to the bowl, the loop has to be installed between the pump and the bowl (putting it in the intake line between the thru-hull and pump will prevent the toilet from priming)...which requires replacing that short piece of hose with two pieces long enough to put the loop where it needs to be.

On electric toilets that don't have any connecting line between the pump and the bowl, the loop has to be in the intake line...which requires an electric solenoid valve in the loop that's wired to the flush button. The valve closes when the flush button is pushed to allow the toilet to prime, opens when the flush button is released to break any siphon.

The first photo is a vented loop with the solenoid valve. The second one shows where vented loops are installed on most sailboats. The small one is the intake loop, the large one is in the discharge line, needed only if the toilet is plumbed to flush directly overboard.

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"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein
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Old 09-30-2016, 12:30 PM   #7
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I agree totally and have already indicated the need for the vented loop, but trying to get him to deal with it is fruitless!!!
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Old 09-30-2016, 12:37 PM   #8
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If he's lucky he'll deal with it the first time he notices that the shoes in his cabin are afloat instead of when he gets the call from the marina that his boat has sunk in its slip. You're welcome to print out my post above and give it to him...prob'ly won't do any good, but it can't do any harm.

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