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Discussion Starter #1
I posted some time ago about discovering a weird box with a red button hidden above the head in my boat. The thread can be read here: http://www.sailnet.com/forums/gear-maintenance/104250-wtf.html

It was surmised that the button was a tank alarm or a macerator pump switch. Well, today I finally had time to disassemble the frame holding the water tank in. This is what I found under the tank:
 

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Discussion Starter #2
The box with the red button was wired to the fitting in the last picture. Can someone help identify what this is? I'm guessing that it's a sensor that activates the alarm when the tank gets full? There was no macerator pump and the only way to empty the tank is to manually pump it overboard.
 

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It is possible that, as the tank is above the head, that it was designed for gravity draining - by far the simplest system.

It does look like a sensor to warn of a n almost full tank.
 

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That sensor looks like it is on the bottom of the tank? Then it would be to tell you when you are out of water. IMO
 

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I'm going with a 'tank full' sensor - that's the 'alarm' condition on a holding tank (to me it looks like the sensor is at the top of the tank)

The liquid in the holding tank would be highly conductive.. it would complete the cct across those two screws; I'm guessing that if you push the red button, that round silver bit might be a buzzer.. the button is a 'check tank' function. If the box buzzes when you press the button the tank's full.
 

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Discussion Starter #6
I'm going with a 'tank full' sensor - that's the 'alarm' condition on a holding tank (to me it looks like the sensor is at the top of the tank)

The liquid in the holding tank would be highly conductive.. it would complete the cct across those two screws; I'm guessing that if you push the red button, that round silver bit might be a buzzer.. the button is a 'check tank' function. If the box buzzes when you press the button the tank's full.
The sensor is, indeed, on the top of the tank. Earlier I had confirmed that there is power in the wire attached to it. However, I placed the sensor in a cup of sea water and could not get the alarm to sound. I'm assuming that at 45 years old, the components have simply ceased to function. I was hoping to be able to rehabilitate the system, but, now I'm leaning toward yanking the whole thing and installing the port-a-potty that I have already purchased. I just don't know if this should be done in the water and I can't afford pulling the valves and glassing over the holes right now. Maybe next year. The valves seem sound and I have read/seen corks being wedged in to the throat of a closed valve as a safety precaution.
 

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That black box looks like a standard project box and home made setup. Can you remove the cover and take a picture of what is inside?
 

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Looks like a pushbutton, a buzzer and a potentiometer (volume control maybe??)
 
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Maybe not potentiometer, but a push button rotary on off switch.
 

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If those two larger wires with the gray covered wire is a direct connection to the sensor then we are missing the power feed.
 

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Looks like a pushbutton, a buzzer and a potentiometer (volume control maybe??)
You are correct it is a potentiometer. You can see the hole and pin to keep the body of the potentiometer from turning. It might have an off position.
 

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... or a red lamp, a buzzer and the test pushbutton... ;)
 

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Discussion Starter #14
At this point it can be agreed that this was, at one time, an internal holding tank with an alarm that would signal when it required pumping out. Because there is no deck pump out, we can then assume that when the alarm went off, the manual pump mounted above the head was used to pump the holding tank overboard, which may have been legal in 1969, but no longer remains so close to shore, which is exactly where this boat will be sailed. So, it will be my intention to remove this entire system, tank and all.
My main concern then becomes how to safely plug the water inlet and the waste output valves without a complete haul out. Both valves appear to be in working order (when closed they do not leak), however, I need to know whether it's prudent, or safe, to remove the hoses from the valves and then plug said valves with cork. Thoughts on this approach?
 

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Buy threaded pipe plugs that are the same thread as the valves. Available in bronze, stainless, or plastic.

Much more positive than a cork.
 
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